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Message-Id: <20141106.144057.541605315482589279.davem@davemloft.net> Date: Thu, 06 Nov 2014 14:40:57 -0500 (EST) From: David Miller <davem@...emloft.net> To: david.vrabel@...rix.com Cc: netdev@...r.kernel.org, xen-devel@...ts.xenproject.org, ian.campbell@...rix.com, wei.liu2@...rix.com, malcolm.crossley@...rix.com Subject: Re: [PATCHv2 net-next] xen-netback: remove unconditional __pskb_pull_tail() in guest Tx path From: David Vrabel <david.vrabel@...rix.com> Date: Wed, 5 Nov 2014 10:50:22 +0000 > From: Malcolm Crossley <malcolm.crossley@...rix.com> > > Unconditionally pulling 128 bytes into the linear area is not required > for: > > - security: Every protocol demux starts with pskb_may_pull() to pull > frag data into the linear area, if necessary, before looking at > headers. > > - performance: Netback has already grant copied up-to 128 bytes from > the first slot of a packet into the linear area. The first slot > normally contain all the IPv4/IPv6 and TCP/UDP headers. > > The unconditional pull would often copy frag data unnecessarily. This > is a performance problem when running on a version of Xen where grant > unmap avoids TLB flushes for pages which are not accessed. TLB > flushes can now be avoided for > 99% of unmaps (it was 0% before). > > Grant unmap TLB flush avoidance will be available in a future version > of Xen (probably 4.6). > > Signed-off-by: Malcolm Crossley <malcolm.crossley@...rix.com> > Signed-off-by: David Vrabel <david.vrabel@...rix.com> Applied, thanks. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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