Re: [PATCH 0/5] vhost: support upto 509 memory regions

Michael S. Tsirkin
2015-06-16T21:16:13Z

On Tue, Jun 16, 2015 at 06:33:34PM +0200, Igor Mammedov wrote:
> Series extends vhost to support upto 509 memory regions,
> and adds some vhost:translate_desc() performance improvemnts
> so it won't regress when memslots are increased to 509.
>
> It fixes running VM crashing during memory hotplug due
> to vhost refusing accepting more than 64 memory regions.
>
> It's only host kernel side fix to make it work with QEMU
> versions that support memory hotplug. But I'll continue
> to work on QEMU side solution to reduce amount of memory
> regions to make things even better.

I'm concerned userspace work will be harder, in particular,
performance gains will be harder to measure.
How about a flag to disable caching?

> Performance wise for guest with (in my case 3 memory regions)
> and netperf's UDP_RR workload translate_desc() execution
> time from total workload takes:
>
> Memory |1G RAM|cached|non cached
> regions # | 3 | 53 | 53
> ------------------------------------
> upstream | 0.3% | - | 3.5%
> ------------------------------------
> this series | 0.2% | 0.5% | 0.7%
>
> where "non cached" column reflects trashing wokload
> with constant cache miss. More details on timing in
> respective patches.
>
> Igor Mammedov (5):
> vhost: use binary search instead of linear in find_region()
> vhost: extend memory regions allocation to vmalloc
> vhost: support upto 509 memory regions
> vhost: add per VQ memory region caching
> vhost: translate_desc: optimization for desc.len < region size
>
> drivers/vhost/vhost.c | 95 +++++++++++++++++++++++++++++++++++++--------------
> drivers/vhost/vhost.h | 1 +
> 2 files changed, 71 insertions(+), 25 deletions(-)
>
> --
> 1.8.3.1