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From: David Laight <David.Laight@ACULAB.COM>
To: 'Paul Durrant' <Paul.Durrant@citrix.com>,
	Sander Eikelenboom <linux@eikelenboom.it>
Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	Ian Campbell <Ian.Campbell@citrix.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: [PATCH net v2 1/3] xen-netback: remove pointless clause from if statement
Date: Fri, 28 Mar 2014 10:35:58 +0000	[thread overview]
Message-ID: <063D6719AE5E284EB5DD2968C1650D6D0F6EB72D__7025.9086824537$1396003102$gmane$org@AcuExch.aculab.com> (raw)
In-Reply-To: <9AAE0902D5BC7E449B7C8E4E778ABCD029E138@AMSPEX01CL01.citrite.net>

From: Paul Durrant
> > A reasonable high estimate for the number of slots required for a specific
> > message is 'frag_count + total_size/4096'.
> > So if that are that many slots free it is definitely ok to add the message.
> >
> 
> Hmm, that may work. By total_size, I assume you mean skb->len, so that calculation is based on an
> overhead of 1 non-optimally packed slot per frag. There'd still need to be a +1 for the GSO 'extra'
> though.

Except I meant '2 * frag_count + size/4096' :-(

You have to assume that every fragment starts at n*4096-1 (so need
at least two slots). A third slot is only needed for fragments
longer that 1+4096+2 - but an extra one is needed for every
4096 bytes after that.

	David

  reply	other threads:[~2014-03-28 10:35 UTC|newest]

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-03-27 12:56 [PATCH net v2 0/3] xen-netback: fix rx slot estimation Paul Durrant
2014-03-27 12:56 ` [PATCH net v2 1/3] xen-netback: remove pointless clause from if statement Paul Durrant
2014-03-27 12:56 ` Paul Durrant
2014-03-27 13:45   ` Sander Eikelenboom
2014-03-27 13:45   ` Sander Eikelenboom
2014-03-27 13:54     ` Paul Durrant
2014-03-27 13:54     ` Paul Durrant
2014-03-27 14:02       ` Sander Eikelenboom
2014-03-27 14:09         ` Paul Durrant
2014-03-27 14:29           ` Sander Eikelenboom
2014-03-27 14:29           ` Sander Eikelenboom
2014-03-27 14:38             ` Paul Durrant
2014-03-27 14:38             ` Paul Durrant
2014-03-27 16:46           ` Sander Eikelenboom
2014-03-27 16:54             ` Paul Durrant
2014-03-27 17:15               ` Sander Eikelenboom
2014-03-27 17:26                 ` Paul Durrant
2014-03-27 17:26                 ` Paul Durrant
2014-03-27 18:34                   ` Sander Eikelenboom
2014-03-27 19:22                     ` [Xen-devel] " Sander Eikelenboom
2014-03-28  9:30                       ` Paul Durrant
2014-03-28  9:30                       ` [Xen-devel] " Paul Durrant
2014-03-28  9:39                         ` Sander Eikelenboom
2014-03-28  9:47                           ` Paul Durrant
2014-03-28  9:59                             ` Sander Eikelenboom
2014-03-28 10:12                               ` Paul Durrant
2014-03-28 10:36                                 ` Sander Eikelenboom
2014-03-28 10:36                                 ` [Xen-devel] " Sander Eikelenboom
2014-03-28 10:12                               ` Paul Durrant
2014-03-28  9:59                             ` Sander Eikelenboom
2014-03-28 10:01                             ` David Laight
2014-03-28 10:01                             ` [Xen-devel] " David Laight
2014-03-28 10:20                               ` Paul Durrant
2014-03-28 10:35                                 ` David Laight [this message]
2014-03-28 10:35                                 ` David Laight
2014-03-28 10:42                                   ` Sander Eikelenboom
2014-03-28 10:42                                   ` [Xen-devel] " Sander Eikelenboom
2014-03-28 10:47                                     ` Paul Durrant
2014-03-28 10:47                                     ` [Xen-devel] " Paul Durrant
2014-03-28 10:53                                       ` Sander Eikelenboom
2014-03-28 10:53                                       ` [Xen-devel] " Sander Eikelenboom
2014-03-28 11:11                                     ` David Laight
2014-03-28 11:35                                       ` Sander Eikelenboom
2014-03-28 11:35                                       ` Sander Eikelenboom
2014-03-28 11:11                                     ` David Laight
2014-03-28 10:44                                   ` Paul Durrant
2014-03-28 10:44                                   ` [Xen-devel] " Paul Durrant
2014-03-28 10:20                               ` Paul Durrant
2014-03-28  9:47                           ` Paul Durrant
2014-03-28  9:39                         ` Sander Eikelenboom
2014-03-27 19:22                     ` Sander Eikelenboom
2014-03-28  0:55                     ` Sander Eikelenboom
2014-03-28  0:55                     ` [Xen-devel] " Sander Eikelenboom
2014-03-28  9:36                       ` Paul Durrant
2014-03-28  9:36                       ` [Xen-devel] " Paul Durrant
2014-03-28  9:46                         ` Sander Eikelenboom
2014-03-28  9:46                         ` [Xen-devel] " Sander Eikelenboom
2014-03-27 18:34                   ` Sander Eikelenboom
2014-03-27 17:15               ` Sander Eikelenboom
2014-03-27 16:54             ` Paul Durrant
2014-03-27 16:46           ` Sander Eikelenboom
2014-03-27 14:09         ` Paul Durrant
2014-03-27 14:02       ` Sander Eikelenboom
2014-03-27 14:00     ` Paul Durrant
2014-03-27 14:05       ` Sander Eikelenboom
2014-03-27 14:05       ` Sander Eikelenboom
2014-03-27 14:00     ` Paul Durrant
2014-03-27 12:56 ` [PATCH net v2 2/3] xen-netback: worse-case estimate in xenvif_rx_action is underestimating Paul Durrant
2014-03-27 12:56 ` Paul Durrant
2014-03-27 12:56 ` [PATCH net v2 3/3] xen-netback: BUG_ON in xenvif_rx_action() not catching overflow Paul Durrant
2014-03-27 12:56 ` Paul Durrant

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