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

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Date:	Tue, 16 Jun 2015 23:16:07 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Igor Mammedov <imammedo@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	pbonzini@...hat.com
Subject: Re: [PATCH 0/5] vhost: support upto 509 memory regions

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
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