All of lore.kernel.org
 help / color / mirror / Atom feed
From: Rusty Russell <rusty@rustcorp.com.au>
To: "Michael S. Tsirkin" <mst@redhat.com>, linux-kernel@vger.kernel.org
Cc: Carsten Otte <cotte@de.ibm.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	linux390@de.ibm.com, Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Shirley Ma <xma@us.ibm.com>,
	lguest@lists.ozlabs.org, linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org, linux-s390@vger.kernel.org,
	kvm@vger.kernel.org, Krishna Kumar <krkumar2@in.ibm.com>,
	Tom Lendacky <tahm@linux.vnet.ibm.com>,
	steved@us.ibm.com, habanero@linux.vnet.ibm.com
Subject: Re: [PATCH RFC 2/3] virtio_net: fix tx capacity checks using new API
Date: Thu, 02 Jun 2011 11:40:26 +0930	[thread overview]
Message-ID: <87vcwphtkd.fsf@rustcorp.com.au> (raw)
In-Reply-To: <110045d5bf250e6ed9c739f8cc6adbbf54e3cc9c.1306921434.git.mst@redhat.com>

On Wed, 1 Jun 2011 12:49:54 +0300, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> In the (rare) case where new descriptors are used
> while virtio_net enables vq callback for the TX vq,
> virtio_net uses the number of sg entries in the skb it frees to
> calculate how many descriptors in the ring have just been made
> available.  But this value is an overestimate: with indirect buffers
> each skb only uses one descriptor entry, meaning we may wake the queue
> only to find we still can't transmit anything.

This is a bit misleading.

The value is an overestimate, but so is the requirement for
2+MAX_SKB_FRAGS, *unless* we suddenly drop into direct mode due to OOM.

Thanks,
Rusty.

WARNING: multiple messages have this Message-ID (diff)
From: Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>
To: "Michael S. Tsirkin"
	<mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Cc: Krishna Kumar <krkumar2-xthvdsQ13ZrQT0dZR+AlfA@public.gmane.org>,
	Carsten Otte <cotte-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>,
	lguest-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org,
	Shirley Ma <xma-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>,
	kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-s390-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	habanero-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org,
	Heiko Carstens
	<heiko.carstens-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	virtualization-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org,
	steved-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org,
	Christian Borntraeger
	<borntraeger-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>,
	Tom Lendacky
	<tahm-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>,
	Martin Schwidefsky
	<schwidefsky-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>,
	linux390-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org
Subject: Re: [PATCH RFC 2/3] virtio_net: fix tx capacity checks using new API
Date: Thu, 02 Jun 2011 11:40:26 +0930	[thread overview]
Message-ID: <87vcwphtkd.fsf@rustcorp.com.au> (raw)
In-Reply-To: <110045d5bf250e6ed9c739f8cc6adbbf54e3cc9c.1306921434.git.mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

On Wed, 1 Jun 2011 12:49:54 +0300, "Michael S. Tsirkin" <mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
> In the (rare) case where new descriptors are used
> while virtio_net enables vq callback for the TX vq,
> virtio_net uses the number of sg entries in the skb it frees to
> calculate how many descriptors in the ring have just been made
> available.  But this value is an overestimate: with indirect buffers
> each skb only uses one descriptor entry, meaning we may wake the queue
> only to find we still can't transmit anything.

This is a bit misleading.

The value is an overestimate, but so is the requirement for
2+MAX_SKB_FRAGS, *unless* we suddenly drop into direct mode due to OOM.

Thanks,
Rusty.

  parent reply	other threads:[~2011-06-02  3:55 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-06-01  9:49 [PATCH RFC 0/3] virtio and vhost-net capacity handling Michael S. Tsirkin
2011-06-01  9:49 ` Michael S. Tsirkin
2011-06-01  9:49 ` [PATCH RFC 1/3] virtio_ring: add capacity check API Michael S. Tsirkin
2011-06-01  9:49   ` Michael S. Tsirkin
2011-06-02  2:11   ` Rusty Russell
2011-06-02  2:11   ` Rusty Russell
2011-06-02  2:11     ` Rusty Russell
2011-06-02 13:30     ` Michael S. Tsirkin
2011-06-02 13:30     ` Michael S. Tsirkin
2011-06-02 13:30       ` Michael S. Tsirkin
2011-06-01  9:49 ` Michael S. Tsirkin
2011-06-01  9:49 ` [PATCH RFC 2/3] virtio_net: fix tx capacity checks using new API Michael S. Tsirkin
2011-06-01  9:49   ` Michael S. Tsirkin
2011-06-02  2:10   ` Rusty Russell
2011-06-02  2:10   ` Rusty Russell [this message]
2011-06-02  2:10     ` Rusty Russell
2011-06-02 13:28     ` Michael S. Tsirkin
2011-06-02 13:28     ` Michael S. Tsirkin
2011-06-02 13:28       ` Michael S. Tsirkin
2011-06-01  9:49 ` Michael S. Tsirkin
2011-06-01  9:50 ` [PATCH RFC 3/3] virtio_net: limit xmit polling Michael S. Tsirkin
2011-06-01  9:50 ` Michael S. Tsirkin
2011-06-01  9:50   ` Michael S. Tsirkin
2011-06-02  3:54   ` Rusty Russell
2011-06-02  3:54   ` Rusty Russell
2011-06-02  3:54     ` Rusty Russell
2011-06-02 13:34     ` Michael S. Tsirkin
2011-06-02 13:34     ` Michael S. Tsirkin
2011-06-02 13:34       ` Michael S. Tsirkin
2011-06-02 14:17       ` Krishna Kumar2
2011-06-02 14:17         ` Krishna Kumar2
2011-06-02 14:43         ` Michael S. Tsirkin
2011-06-02 14:43         ` Michael S. Tsirkin
2011-06-02 14:43           ` Michael S. Tsirkin
2011-06-02 15:26           ` Krishna Kumar2
2011-06-02 15:26           ` Krishna Kumar2
2011-06-02 15:26             ` Krishna Kumar2
2011-06-02 15:34             ` Michael S. Tsirkin
2011-06-02 15:34             ` Michael S. Tsirkin
2011-06-02 15:34               ` Michael S. Tsirkin
2011-06-03  4:08               ` Krishna Kumar2
2011-06-03  4:08               ` Krishna Kumar2
2011-06-02 15:44             ` Michael S. Tsirkin
2011-06-02 15:44               ` Michael S. Tsirkin
2011-06-02 15:44             ` Michael S. Tsirkin
2011-06-02 14:17       ` Krishna Kumar2

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=87vcwphtkd.fsf@rustcorp.com.au \
    --to=rusty@rustcorp.com.au \
    --cc=borntraeger@de.ibm.com \
    --cc=cotte@de.ibm.com \
    --cc=habanero@linux.vnet.ibm.com \
    --cc=heiko.carstens@de.ibm.com \
    --cc=krkumar2@in.ibm.com \
    --cc=kvm@vger.kernel.org \
    --cc=lguest@lists.ozlabs.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-s390@vger.kernel.org \
    --cc=linux390@de.ibm.com \
    --cc=mst@redhat.com \
    --cc=netdev@vger.kernel.org \
    --cc=schwidefsky@de.ibm.com \
    --cc=steved@us.ibm.com \
    --cc=tahm@linux.vnet.ibm.com \
    --cc=virtualization@lists.linux-foundation.org \
    --cc=xma@us.ibm.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.