Re: [RFC PATCH V3 0/5] Hi:

Jason Wang
2019-01-07T06:58:08Z

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
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