linux-kernel - Re: [RFC PATCH 1/1] vhost: TX used buffer guest signal accumulation

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Message-ID: <1288294355.11251.20.camel@localhost.localdomain>
Date:	Thu, 28 Oct 2010 12:32:35 -0700
From:	Shirley Ma <mashirle@...ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/1] vhost: TX used buffer guest signal accumulation

On Thu, 2010-10-28 at 07:20 +0200, Michael S. Tsirkin wrote:
> My concern is this can delay signalling for unlimited time.
> Could you pls test this with guests that do not have
> 2b5bbe3b8bee8b38bdc27dd9c0270829b6eb7eeb
> b0c39dbdc204006ef3558a66716ff09797619778
> that is 2.6.31 and older? 

The patch only induces delay signaling unlimited time when there is no
TX packet to transmit. I thought TX signaling only noticing guest to
release the used buffers, anything else beside this?

I tested rhel5u5 guest (2.6.18 kernel), it works fine. I checked the two
commits log, I don't think this patch could cause any issue w/o these
two patches.

Also I found a big TX regression for old guest and new guest. For old
guest, I am able to get almost 11Gb/s for 2K message size, but for the
new guest kernel, I can only get 3.5 Gb/s with the patch and same host.
I will dig it why.

thanks
Shirley

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