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308 lines
8.9 KiB
C
308 lines
8.9 KiB
C
/* pvrdtscp algorithm
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*
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* This sample code demonstrates the use of the paravirtualized rdtscp
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* algorithm. Using this algorithm, an application may communicate with
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* the Xen hypervisor (version 4.0+) to obtain timestamp information which
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* is both monotonically increasing and has a fixed 1 GHz rate, even across
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* migrations between machines with different TSC rates and offsets.
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* Further,the algorithm provides performance near the performance of a
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* native rdtsc/rdtscp instruction -- much faster than emulation PROVIDED
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* the application is running on a machine on which the rdtscp instruction
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* is supported and TSC is "safe". The application must also be running in a
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* PV domain. (HVM domains may be supported at a later time.) On machines
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* where TSC is unsafe or the rdtscp instruction is not supported, Xen
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* (v4.0+) provides emulation which is slower but consistent with the pvrdtscp
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* algorithm, thus providing support for the algorithm for live migration
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* across all machines.
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*
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* More information can be found within the Xen (4.0+) source tree at
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* docs/misc/tscmode.txt
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*
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* Copyright (c) 2009 Oracle Corporation and/or its affiliates.
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* All rights reserved
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* Written by: Dan Magenheimer <dan.magenheimer@oracle.com>
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*
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* This code is derived from code licensed under the GNU
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* General Public License ("GPL") version 2 and is therefore itself
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* also licensed under the GPL version 2.
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*
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* This code is known to compile and run on Oracle Enterprise Linux 5 Update 2
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* using gcc version 4.1.2, but its purpose is to describe the pvrdtscp
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* algorithm and its ABI to Xen version 4.0+
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/wait.h>
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#ifdef __LP64__
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#define __X86_64__
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typedef unsigned short u16;
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typedef unsigned int u32;
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typedef unsigned long u64;
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typedef int i32;
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typedef long i64;
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#define NSEC_PER_SEC 1000000000
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#else
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#define __X86_32__
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typedef unsigned int u16;
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typedef unsigned long u32;
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typedef unsigned long long u64;
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typedef long i32;
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typedef long long i64;
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#define NSEC_PER_SEC 1000000000L
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#endif
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static inline void hvm_cpuid(u32 idx, u32 sub,
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u32 *eax, u32 *ebx, u32 *ecx, u32 *edx)
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{
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*eax = idx, *ecx = sub;
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asm("cpuid" : "=a" (*eax), "=b" (*ebx), "=c" (*ecx), "=d" (*edx)
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: "0" (*eax), "2" (*ecx));
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}
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static inline void pv_cpuid(u32 idx, u32 sub,
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u32 *eax, u32 *ebx, u32 *ecx, u32 *edx)
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{
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*eax = idx, *ecx = sub;
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asm volatile ( "ud2a ; .ascii \"xen\"; cpuid" : "=a" (*eax),
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"=b" (*ebx), "=c" (*ecx), "=d" (*edx) : "0" (*eax), "2" (*ecx));
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}
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static inline u64 do_rdtscp(u32 *aux)
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{
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static u64 last = 0;
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u32 lo32, hi32;
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u64 val;
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asm volatile(".byte 0x0f,0x01,0xf9":"=a"(lo32),"=d"(hi32),"=c" (*aux));
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val = lo32 | ((u64)hi32 << 32);
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return val;
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}
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static inline int get_xen_tsc_mode(void)
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{
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u32 val, dummy1, dummy2, dummy3;
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pv_cpuid(0x40000003,0,&dummy1,&val,&dummy2,&dummy3);
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return val;
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}
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static inline int get_xen_vtsc(void)
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{
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u32 val, dummy1, dummy2, dummy3;
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pv_cpuid(0x40000003,0,&val,&dummy1,&dummy2,&dummy3);
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return val & 1;
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}
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static inline int get_xen_vtsc_khz(void)
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{
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u32 val, dummy1, dummy2, dummy3;
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pv_cpuid(0x40000003,0,&dummy1,&dummy2,&val,&dummy3);
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return val;
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}
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static inline u32 get_xen_cpu_khz(void)
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{
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u32 cpu_khz, dummy1, dummy2, dummy3;
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pv_cpuid(0x40000003,2,&cpu_khz,&dummy1,&dummy2,&dummy3);
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return cpu_khz;
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}
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static inline u32 get_xen_incarnation(void)
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{
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u32 incarn, dummy1, dummy2, dummy3;
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pv_cpuid(0x40000003,0,&dummy1,&dummy2,&dummy3,&incarn);
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return incarn;
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}
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static inline void get_xen_time_values(u64 *offset, u32 *mul_frac, u32 *shift)
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{
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u32 off_lo, off_hi, sys_lo, sys_hi, dummy;
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pv_cpuid(0x40000003,1,&off_lo,&off_hi,mul_frac,shift);
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*offset = off_lo | ((u64)off_hi << 32);
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}
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static inline u64 scale_delta(u64 delta, u32 tsc_mul_frac, i32 tsc_shift)
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{
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u64 product;
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#ifdef __X86_32__
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u32 tmp1, tmp2;
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#endif
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if ( tsc_shift < 0 )
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delta >>= -tsc_shift;
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else
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delta <<= tsc_shift;
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#ifdef __X86_32__
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asm (
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"mul %5 ; "
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"mov %4,%%eax ; "
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"mov %%edx,%4 ; "
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"mul %5 ; "
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"xor %5,%5 ; "
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"add %4,%%eax ; "
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"adc %5,%%edx ; "
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: "=A" (product), "=r" (tmp1), "=r" (tmp2)
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: "a" ((u32)delta), "1" ((u32)(delta >> 32)), "2" (tsc_mul_frac) );
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#else
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asm (
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"mul %%rdx ; shrd $32,%%rdx,%%rax"
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: "=a" (product) : "0" (delta), "d" ((u64)tsc_mul_frac) );
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#endif
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return product;
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}
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static inline u64 get_pvrdtscp_timestamp(int *discontinuity)
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{
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static int firsttime = 1;
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static u64 last_pvrdtscp_timestamp = 0;
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static u32 last_tsc_aux;
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static u64 xen_ns_offset;
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static u32 xen_tsc_to_ns_mul_frac, xen_tsc_to_ns_shift;
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u32 this_tsc_aux;
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u64 timestamp, cur_tsc, cur_ns;
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if (firsttime) {
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cur_tsc = do_rdtscp(&last_tsc_aux);
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get_xen_time_values(&xen_ns_offset, &xen_tsc_to_ns_mul_frac,
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&xen_tsc_to_ns_shift);
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cur_ns = scale_delta(cur_tsc, xen_tsc_to_ns_mul_frac,
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xen_tsc_to_ns_shift);
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timestamp = cur_ns - xen_ns_offset;
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last_pvrdtscp_timestamp = timestamp;
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firsttime = 0;
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}
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cur_tsc = do_rdtscp(&this_tsc_aux);
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*discontinuity = 0;
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while (this_tsc_aux != last_tsc_aux) {
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/* if tsc_aux changed, try again */
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last_tsc_aux = this_tsc_aux;
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get_xen_time_values(&xen_ns_offset, &xen_tsc_to_ns_mul_frac,
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&xen_tsc_to_ns_shift);
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cur_tsc = do_rdtscp(&this_tsc_aux);
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*discontinuity = 1;
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}
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/* compute nsec from TSC and Xen time values */
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cur_ns = scale_delta(cur_tsc, xen_tsc_to_ns_mul_frac,
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xen_tsc_to_ns_shift);
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timestamp = cur_ns - xen_ns_offset;
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/* enforce monotonicity just in case */
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if ((i64)(timestamp - last_pvrdtscp_timestamp) > 0)
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last_pvrdtscp_timestamp = timestamp;
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else {
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/* this should never happen but we'll check it anyway in
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* case of some strange combination of scaling errors
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* occurs across a very fast migration */
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printf("Time went backwards by %lluns\n",
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(unsigned long long)(last_pvrdtscp_timestamp-timestamp));
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timestamp = ++last_pvrdtscp_timestamp;
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}
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return timestamp;
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}
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#define HVM 1
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#define PVM 0
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static int running_on_xen(int hvm, u16 *version_major, u16 *version_minor)
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{
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u32 eax, ebx, ecx, edx, base;
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union { char csig[16]; u32 u[4]; } sig;
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for (base=0x40000000; base < 0x40010000; base += 0x100) {
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if (hvm==HVM)
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hvm_cpuid(base,0,&eax,&ebx,&ecx,&edx);
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else
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pv_cpuid(base,0,&eax,&ebx,&ecx,&edx);
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sig.u[0] = ebx; sig.u[1] = ecx; sig.u[2] = edx;
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sig.csig[12] = '\0';
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if (!strcmp("XenVMMXenVMM",&sig.csig[0]) && (eax >= (base+2))) {
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if (hvm==HVM)
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hvm_cpuid(base+1,0,&eax,&ebx,&ecx,&edx);
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else
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pv_cpuid(base+1,0,&eax,&ebx,&ecx,&edx);
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*version_major = (eax >> 16) & 0xffff;
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*version_minor = eax & 0xffff;
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return 1;
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}
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}
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return 0;
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}
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main(int ac, char **av)
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{
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u32 dummy;
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u16 version_hi, version_lo;
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u64 ts, last_ts;
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int status, discontinuity = 0;
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pid_t pid;
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if (running_on_xen(HVM,&version_hi,&version_lo)) {
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printf("running on Xen v%d.%d as an HVM domain, "
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"pvrdtsc not supported, exiting\n",
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(int)version_hi, (int)version_lo);
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exit(0);
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}
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pid = fork();
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if (pid == -1) {
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fprintf(stderr,"Huh? Fork failed\n");
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return 0;
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}
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else if (pid == 0) { /* child */
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pv_cpuid(0x40000000,0,&dummy,&dummy,&dummy,&dummy);
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exit(0);
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}
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waitpid(pid,&status,0);
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if (!WIFEXITED(status))
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exit(0);
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if (!running_on_xen(PVM,&version_hi,&version_lo)) {
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printf("not running on Xen, exiting\n");
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exit(0);
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}
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printf("running on Xen v%d.%d as a PV domain\n",
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(int)version_hi, (int)version_lo);
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if ( version_hi <= 3 ) {
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printf("pvrdtscp requires Xen version 4.0 or greater\n");
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/* exit(0); FIXME after xen-unstable is officially v4.0 */
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}
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if ( get_xen_tsc_mode() != 3 )
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printf("tsc_mode not pvrdtscp, set tsc_mode=3, exiting\n");
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/* OK, we are on Xen, now loop forever checking timestamps */
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ts = get_pvrdtscp_timestamp(&discontinuity);
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printf("Starting with ts=%lluns 0x%llx (%llusec)\n",ts,ts,ts/NSEC_PER_SEC);
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printf("incarn=%d: vtsc=%d, vtsc_khz=%lu, phys cpu_khz=%lu\n",
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(unsigned long)get_xen_incarnation(),
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(unsigned long)get_xen_vtsc(),
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(unsigned long)get_xen_vtsc_khz(),
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(unsigned long)get_xen_cpu_khz());
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ts = get_pvrdtscp_timestamp(&discontinuity);
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last_ts = ts;
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while (1) {
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ts = get_pvrdtscp_timestamp(&discontinuity);
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if (discontinuity)
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printf("migrated/restored, incarn=%d: "
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"vtsc now %d, vtsc_khz=%lu, phys cpu_khz=%lu\n",
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(unsigned long)get_xen_incarnation(),
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(unsigned long)get_xen_vtsc(),
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(unsigned long)get_xen_vtsc_khz(),
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(unsigned long)get_xen_cpu_khz());
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if (ts < last_ts)
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/* this should NEVER happen, especially since there
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* is a check for it in get_pvrdtscp_timestamp() */
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printf("Time went backwards: %lluns (%llusec)\n",
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last_ts-ts,(last_ts-ts)/NSEC_PER_SEC);
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if (ts > last_ts + 200000000LL)
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/* this is OK, usually about 2sec for save/restore
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* and a fraction of a second for live migrate */
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printf("Time jumped forward %lluns (%llusec)\n",
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ts-last_ts,(ts-last_ts)/NSEC_PER_SEC);
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last_ts = ts;
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}
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}
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