linux-kernel - Re: [RFC PATCH V2 0/5] vhost: accelerate metadata access through vmap()

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Date:   Fri, 8 Mar 2019 06:12:20 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, peterx@...hat.com,
        linux-mm@...ck.org, aarcange@...hat.com,
        linux-arm-kernel@...ts.infradead.org, linux-parisc@...r.kernel.org
Subject: Re: [RFC PATCH V2 0/5] vhost: accelerate metadata access through
 vmap()

On Wed, Mar 06, 2019 at 02:18:07AM -0500, 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. This is done through setup kernel address through vmap() and
> resigter MMU notifier for invalidation.
> 
> Test shows about 24% improvement on TX PPS. TCP_STREAM doesn't see
> obvious improvement.

How is this going to work for CPUs with virtually tagged caches?