linux-kernel - Re: [RFC PATCH V3 0/5] Hi:

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Message-ID: <68727e1b-1d51-0596-29c3-931475dd5dab@redhat.com>
Date:   Mon, 7 Jan 2019 14:58:08 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        davem@...emloft.net
Subject: Re: [RFC PATCH V3 0/5] Hi:


On 2019/1/5 上午5:41, Michael S. Tsirkin wrote:
> On Sat, Dec 29, 2018 at 08:46:51PM +0800, Jason Wang wrote:
>> This series tries to access virtqueue metadata through kernel virtual
>> address instead of copy_user() friends since they had too much
>> overheads like checks, spec barriers or even hardware feature
>> toggling.
>
> I think it's a reasonable approach.
> However I need to look at whether and which mmu notifiers are invoked before
> writeback. Do you know?


I don't know but just looking at the MMU notifier ops definition, 
there's no such callback if my understanding is correct.

Thanks


>
>> Test shows about 24% improvement on TX PPS. It should benefit other
>> cases as well.
>>
>> Changes from V2:
>> - fix buggy range overlapping check
>> - tear down MMU notifier during vhost ioctl to make sure invalidation
>>    request can read metadata userspace address and vq size without
>>    holding vq mutex.
>> Changes from V1:
>> - instead of pinning pages, use MMU notifier to invalidate vmaps and
>>    remap duing metadata prefetch
>> - fix build warning on MIPS
>>
>> Jason Wang (5):
>>    vhost: generalize adding used elem
>>    vhost: fine grain userspace memory accessors
>>    vhost: rename vq_iotlb_prefetch() to vq_meta_prefetch()
>>    vhost: introduce helpers to get the size of metadata area
>>    vhost: access vq metadata through kernel virtual address
>>
>>   drivers/vhost/net.c   |   4 +-
>>   drivers/vhost/vhost.c | 416 +++++++++++++++++++++++++++++++++++++-----
>>   drivers/vhost/vhost.h |  15 +-
>>   3 files changed, 384 insertions(+), 51 deletions(-)
>>
>> -- 
>> 2.17.1