lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Fri, 14 Jan 2022 14:38:16 +0100
From:   Stefano Garzarella <>
To:     "Michael S. Tsirkin" <>
        Jason Wang <>
Subject: Re: [PATCH v1] vhost: cache avail index in vhost_enable_notify()

On Fri, Jan 14, 2022 at 07:45:35AM -0500, Michael S. Tsirkin wrote:
>On Fri, Jan 14, 2022 at 10:05:08AM +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.
>> We are not caching the avail index, so when the device will call
>> vhost_get_vq_desc(), it will find the old value in the cache and
>> it will read the avail index again.
>> It would be better to refresh the cache every time we read avail
>> index, so let's change vhost_enable_notify() caching the value in
>> `avail_idx` and compare it with `last_avail_idx` to check if there
>> are new buffers available.
>> Anyway, we don't expect a significant performance boost because
>> the above path is not very common, indeed vhost_enable_notify()
>> is often called with unlikely(), expecting that avail index has
>> not been updated.
>> Signed-off-by: Stefano Garzarella <>
>... and can in theory even hurt due to an extra memory write.
>So ... performance test restults pls?

Right, could be.

I'll run some perf test with vsock, about net, do you have a test suite 
or common step to follow to test it?


Powered by blists - more mailing lists