On 06/24/2010 06:42 AM, Avi Kivity wrote:
On 06/24/2010 02:34 PM, Andre Przywara wrote:
Non-anonymous memory doesn't work well with ksm and transparent
hugepages. Is it possible to use anonymous memory rather than file
backed?
I'd prefer non-file backed, too. But that is how the current huge
pages implementation is done. We could use MAP_HUGETLB and declare
NUMA _and_ huge pages as 2.6.32+ only. Unfortunately I didn't find an
easy way to detect the presence of the MAP_HUGETLB flag. If the
kernel does not support it, it seems that mmap silently ignores it
and uses 4KB pages instead.
That sucks, unfortunately it is normal practice. However it is a soft
failure, everything works just a bit slower. So it's probably
acceptable.
To avoid this I'd like to see the pinning done from within QEMU. I
am not sure whether calling numactl via system() and friends is OK,
I'd prefer to run the syscalls directly (like in patch 3/3) and
pull the necessary options into the -numa pin,... command line. We
could mimic numactl's syntax here.
Definitely not use system(), but IIRC numactl has a library interface?
Right, that is what I include in patch 3/3 and use. I got the
impression Anthony wanted to avoid reimplementing parts of numactl,
especially enabling the full flexibility of the command line
interface (like specifying nodes, policies and interleaving).
I want QEMU to use the library and pull the necessary options into
the -numa pin,... parsing, even if this means duplicating numactl
functionality.
I agree with that. It's a lot easier to use a single tool than to try
to integrate things yourself, the unix tradition of grep | sort | uniq
-c | sort -n notwithstanding. Especially when one of the tools is qemu.
I could disagree more here. This is why we don't support CPU pinning
and instead provide PID information for each VCPU thread.
The folks that want to use pinning are not notice users. They are not
going to be happy unless you can make full use of existing tools. That
means replicating all of numactl's functionality (which is not what the
current patches do) or enable numactl to be used with a guest.
Regards,
Anthony Liguori
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