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bitkeeper revision 1.144 (3e74d2c4Sp8uQ7JRHj5sf5cI7xOMQA)

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Merge scramble.cl.cam.ac.uk:/usr/groups/xeno/BK/xeno.bk
into scramble.cl.cam.ac.uk:/local/scratch/kaf24/xeno
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kaf24@scramble.cl.cam.ac.uk committed 2003-03-16 19:38:44 +00:00
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.rootkeys
+1
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@@ -193,6 +193,7 @@
3ddb79bcbOVHh38VJzc97-JEGD4dJQ xen/Makefile
3ddb79bcCa2VbsMp7mWKlhgwLQUQGA xen/README
3ddb79bcWnTwYsQRWl_PaneJfa6p0w xen/Rules.mk
3e74d2be6ELqhaY1sW0yyHRKhpOvDQ xen/TODO
3ddb79bcZbRBzT3elFWSX7u6NtMagQ xen/arch/i386/Makefile
3ddb79bcBQF85CfLS4i1WGZ4oLLaCA xen/arch/i386/Rules.mk
3e5636e5FAYZ5_vQnmgwFJfSdmO5Mw xen/arch/i386/acpitable.c
xen/README
+3 -111
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@@ -1,110 +1,17 @@
*****************************************************
Xeno Hypervisor (18/7/02)
Xeno Hypervisor (16/3/03)
1) Tree layout
Looks rather like a simplified Linux :-)
Headers are in include/xeno and include asm-<arch>.
At build time we create symlinks:
include/linux -> include/xeno
include/asm -> include/asm-<arch>
In this way, Linux device drivers should need less tweaking of
their #include lines.
For source files, mapping between hypervisor and Linux is:
Linux Hypervisor
----- ----------
kernel/init/mm/lib -> common
net/* -> net/*
drivers/* -> drivers/*
arch/* -> arch/*
Note that the use of #include <asm/...> and #include <linux/...> can
lead to confusion, as such files will often exist on the system include
path, even if a version doesn't exist within the hypervisor tree.
Unfortunately '-nostdinc' cannot be specified to the compiler, as that
prevents us using stdarg.h in the compiler's own header directory.
We try to not modify things in driver/* as much as possible, so we can
easily take updates from Linux. arch/* is basically straight from
Linux, with fingers in Linux-specific pies hacked off. common/* has
a lot of Linux code in it, but certain subsystems (task maintenance,
low-level memory handling) have been replaced. net/* contains enough
Linux-like gloop to get network drivers to work with little/no
modification.
2) Building
'make': Builds ELF executable called 'image' in base directory
'make install': gzip-compresses 'image' and copies it to TFTP server
'make clean': removes *all* build and target files
*****************************************************
Random thoughts and stuff from here down...
Todo list
---------
* Hypervisor need only directly map its own memory pool
(maybe 128MB, tops). That would need 0x08000000....
This would allow 512MB Linux with plenty room for vmalloc'ed areas.
* Network device -- port drivers to hypervisor, implement virtual
driver for xeno-linux. Looks like Ethernet.
-- Hypervisor needs to do (at a minimum):
- packet filtering on tx (unicast IP only)
- packet demux on rx (unicast IP only)
- provide DHCP [maybedo something simpler?]
and ARP [at least for hypervisor IP address]
Segment descriptor tables
-------------------------
We want to allow guest OSes to specify GDT and LDT tables using their
own pages of memory (just like with page tables). So allow the following:
* new_table_entry(ptr, val)
[Allows insertion of a code, data, or LDT descriptor into given
location. Can simply be checked then poked, with no need to look at
page type.]
* new_GDT() -- relevent virtual pages are resolved to frames. Either
(i) page not present; or (ii) page is only mapped read-only and checks
out okay (then marked as special page). Old table is resolved first,
and the pages are unmarked (no longer special type).
* new_LDT() -- same as for new_GDT(), with same special page type.
Page table updates must be hooked, so we look for updates to virtual page
addresses in the GDT/LDT range. If map to not present, then old physpage
has type_count decremented. If map to present, ensure read-only, check the
page, and set special type.
Merge set_{LDT,GDT} into update_baseptr, by passing four args:
update_baseptrs(mask, ptab, gdttab, ldttab);
Update of ptab requires update of gtab (or set to internal default).
Update of gtab requires update of ltab (or set to internal default).
The hypervisor page cache
-------------------------
This will allow guest OSes to make use of spare pages in the system, but
allow them to be immediately used for any new domains or memory requests.
The idea is that, when a page is laundered and falls off Linux's clean_LRU
list, rather than freeing it it becomes a candidate for passing down into
the hypervisor. In return, xeno-linux may ask for one of its previously-
cached pages back:
(page, new_id) = cache_query(page, old_id);
If the requested page couldn't be kept, a blank page is returned.
When would Linux make the query? Whenever it wants a page back without
the delay or going to disc. Also, whenever a page would otherwise be
flushed to disc.
To try and add to the cache: (blank_page, new_id) = cache_query(page, NULL);
[NULL means "give me a blank page"].
To try and retrieve from the cache: (page, new_id) = cache_query(x_page, id)
[we may request that x_page just be discarded, and therefore not impinge
on this domain's cache quota].
Booting secondary processors
----------------------------
It's twisty and turny, so this is (roughly) the code path:
start_of_day (i386/setup.c)
smp_boot_cpus (i386/smpboot.c)
* initialises boot CPU data
@@ -128,18 +35,3 @@ On other processor:
* barrier, then write bitmasks to signal back to boot cpu
* then barrel into...
cpu_idle (i386/process.c)
[THIS IS PROBABLY REASONABLE -- BOOT CPU SHOULD KICK
SECONDARIES TO GET WORK DONE]
SMP capabilities
----------------
Current intention is to allow hypervisor to schedule on all processors in
SMP boxen, but to tie each domain to a single processor. This simplifies
many SMP intricacies both in terms of correctness and efficiency (eg.
TLB flushing, network packet delivery, ...).
Clients can still make use of SMP by installing multiple domains on a single
machine, and treating it as a fast cluster (at the very least, the
hypervisor will have fast routing of locally-destined packets).
xen/TODO
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@@ -0,0 +1,129 @@
This is stuff we probably want to implement in the near future. I
think I have them in a sensible priority order -- the first few would
be nice to fix before a code release. The later ones can be
longer-term goals.
-- Keir (16/3/03)
1. ASSIGNING DOMAINS TO PROCESSORS
----------------------------------
More intelligent assignment of domains to processors. In
particular, we don't play well with hyperthreading: we will assign
domains to virtual processors on the same package, rather then
spreading them across processor packages.
What we need to do is port code from Linux which stores information on
relationships between processors in the system (eg. which ones are
siblings in teh same package). We then use this to balance domains
across packages, and across virtual processors within a package.
2. PROPER DESTRUCTION OF DOMAINS
--------------------------------
Currently we do not free resources when destroying a domain. This is
because they may be tied up in subsystems, and there is no way of
pulling them back in a safe manner.
The fix is probably to reference count resources and automatically
free them when the count reaches zero. We may get away with one count
per domain (for all its resources). When this reaches zero we know it
is safe to free everything: block-device rings, network rings, and all
the rest.
3. FIX HANDLING OF NETWORK RINGS
--------------------------------
Handling of the transmit rings is currently very broken (for example,
sending an inter-domain packet will wedge the hypervisor). This is
because we may handle packets out of order (eg. inter-domain packets
are handled eagerly, while packets for real interfaces are queued),
but our current ring design really assumes in-order handling.
A neat fix will be to allow responses to be queued in a different
order to requests, just as we already do with block-device
rings. We'll need to add an opaque identifier to ring entries,
allowing matching of requests and responses, but that's about it.
4. GDT AND LDT VIRTUALISATION
-----------------------------
We do not allow modification of the GDT, or any use of the LDT. This
is necessary for support of unmodified applications (eg. Linux uses
LDT in threaded applications, while Windows needs to update GDT
entries).
I have some text on how to do this:
/usr/groups/xeno/discussion-docs/memory_management/segment_tables.txt
It's already half implemented, but the rest is still to do.
5. DOMAIN 0 MANAGEMENT DAEMON
-----------------------------
A better control daemon is required for domain 0, which keeps proper
track of machine resources and can make sensible policy choices. This
may require support in Xen; for example, notifications (eg. DOMn is
killed), and requests (eg. can DOMn allocate x frames of memory?).
6. ACCURATE TIMERS AND WALL-CLOCK TIME
--------------------------------------
Currently our long-term timebase free runs on CPU0, with no external
calibration. We should run ntpd on domain 0 and allow this to warp
Xen's timebase. Once this is done, we can have a timebase per CPU and
not worry about relative drift (since they'll all get sync'ed
periodically by ntp).
7. NEW DESIGN FEATURES
----------------------
This includes the last-chance page cache, and the unified buffer cache.
Graveyard
*********
Following is some description how some of the above might be
implemented. Some of it is superceded and/or out of date, so follow
with caution.
Segment descriptor tables
-------------------------
We want to allow guest OSes to specify GDT and LDT tables using their
own pages of memory (just like with page tables). So allow the following:
* new_table_entry(ptr, val)
[Allows insertion of a code, data, or LDT descriptor into given
location. Can simply be checked then poked, with no need to look at
page type.]
* new_GDT() -- relevent virtual pages are resolved to frames. Either
(i) page not present; or (ii) page is only mapped read-only and checks
out okay (then marked as special page). Old table is resolved first,
and the pages are unmarked (no longer special type).
* new_LDT() -- same as for new_GDT(), with same special page type.
Page table updates must be hooked, so we look for updates to virtual page
addresses in the GDT/LDT range. If map to not present, then old physpage
has type_count decremented. If map to present, ensure read-only, check the
page, and set special type.
Merge set_{LDT,GDT} into update_baseptr, by passing four args:
update_baseptrs(mask, ptab, gdttab, ldttab);
Update of ptab requires update of gtab (or set to internal default).
Update of gtab requires update of ltab (or set to internal default).
The hypervisor page cache
-------------------------
This will allow guest OSes to make use of spare pages in the system, but
allow them to be immediately used for any new domains or memory requests.
The idea is that, when a page is laundered and falls off Linux's clean_LRU
list, rather than freeing it it becomes a candidate for passing down into
the hypervisor. In return, xeno-linux may ask for one of its previously-
cached pages back:
(page, new_id) = cache_query(page, old_id);
If the requested page couldn't be kept, a blank page is returned.
When would Linux make the query? Whenever it wants a page back without
the delay or going to disc. Also, whenever a page would otherwise be
flushed to disc.
To try and add to the cache: (blank_page, new_id) = cache_query(page, NULL);
[NULL means "give me a blank page"].
To try and retrieve from the cache: (page, new_id) = cache_query(x_page, id)
[we may request that x_page just be discarded, and therefore not impinge
on this domain's cache quota].
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