From: Sowmini Varadhan <sowmini.varadhan@oracle•com>
To: David L Stevens <david.stevens@oracle•com>
Cc: netdev@vger•kernel.org
Subject: Re: [PATCH net-next v2 2/2] Re-check for a VIO_DESC_READY data descriptor after short udelay()
Date: Tue, 2 Sep 2014 12:32:38 -0400 [thread overview]
Message-ID: <20140902163238.GD31516@oracle.com> (raw)
In-Reply-To: <5405EFE7.4090302@oracle.com>
On (09/02/14 12:27), David L Stevens wrote:
> Sowmini,
> One of the things I found while looking at the code is that the
> write memory barrier is in the wrong place. I have a patch to fix it, but
> it means the last descriptor will NOT be marked as ready until the cache
> is flushed, which may be delayed.
I see.
I can certainly try that (could you please share that patch offline?)
But this fudge-factored delay (which, fwiw, I too cringed to add)
was actually motivated by some observations on other non-linux OS-es.
> That fix may make this one moot. Maybe not, but certainly there is
> an unnecessary delay in notifying the peer because of that bug. The fix is
> simply to move the "wmb()" after, instead of before, setting VIO_DESC_READY.
> I mentioned it in our stand-up last week, which you couldn't attend, because
> I pointed it out for the VDC driver, which also has the same problem.
>
> You may want to retry with that change to see if the delay still
> helps.
next prev parent reply other threads:[~2014-09-02 16:32 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-02 16:20 [PATCH net-next v2 2/2] Re-check for a VIO_DESC_READY data descriptor after short udelay() Sowmini Varadhan
2014-09-02 16:27 ` David L Stevens
2014-09-02 16:32 ` Sowmini Varadhan [this message]
2014-09-05 5:36 ` David Miller
2014-09-05 13:47 ` Sowmini Varadhan
2014-09-06 21:02 ` Sowmini Varadhan
[not found] ` <20140907181510.GA23753@oracle.com>
2014-09-07 19:36 ` Raghuram Kothakota
2014-09-07 23:19 ` David Miller
2014-09-08 13:45 ` David L Stevens
2014-09-08 14:03 ` Sowmini Varadhan
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