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Date: Thu, 13 Jan 2022 16:44:47 +0100 From: Stefano Garzarella <sgarzare@...hat.com> To: "Michael S. Tsirkin" <mst@...hat.com> Cc: virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org, stefanha@...hat.com, Jason Wang <jasowang@...hat.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org Subject: Re: [RFC PATCH] vhost: cache avail index in vhost_enable_notify() On Thu, Jan 13, 2022 at 10:19:46AM -0500, Michael S. Tsirkin wrote: >On Thu, Jan 13, 2022 at 03:56:42PM +0100, Stefano Garzarella wrote: >> In vhost_enable_notify() we enable the notifications and we read >> the avail index to check if new buffers have become available in >> the meantime. In this case, the device would go to re-read avail >> index to access the descriptor. >> >> As we already do in other place, we can cache the value in `avail_idx` >> and compare it with `last_avail_idx` to check if there are new >> buffers available. >> >> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com> > >I guess we can ... but what's the point? > That without this patch if avail index is new, then device when will call vhost_get_vq_desc() will find old value in cache and will read it again. With this patch we also do the same path and update the cache every time we read avail index. I marked it RFC because I don't know if it's worth it :-) Stefano
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