Re: [Xen-devel] [PATCHv1 net-next] xen-netback: remove unconditional pull_skb_tail in guest Tx path

[David Miller <davem@xxxxxxxxxxxxx>]

From: David Vrabel <david.vrabel@xxxxxxxxxx>
Date: Mon, 3 Nov 2014 17:23:51 +0000

> From: Malcolm Crossley <malcolm.crossley@xxxxxxxxxx>
> 
> Unconditionally pulling 128 bytes into the linear buffer is not
> required. Netback has already grant copied up-to 128 bytes from the
> first slot of a packet into the linear buffer. 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@xxxxxxxxxx>
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>

Now that this has been discussed a bit, it is possible to get an ack or two?

Thanks.

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