Re: [Xen-devel] [PATCH 3/3] grant-table: defer releasing pages acquired in a grant copy

[Tim Deegan <tim@xxxxxxx>]

At 18:19 +0000 on 20 Jan (1421774389), David Vrabel wrote:
> Acquiring a page for the source or destination of a grant copy is an
> expensive operation.  A common use case is for two adjacent grant copy
> ops to operate on either the same source or the same destination page.
> 
> Instead of always acquiring and releasing destination and source pages
> for each operation, release the page once it is no longer valid for
> the next op.
> 
> If either the source or destination domains changes both pages are
> released as it is unlikely that either will still be valid.
> 
> XenServer's performance benchmarks show modest improvements in network
> receive throughput (netback uses grant copy in the guest Rx path) and
> no regressions in disk performamnce (using tapdisk3 which grant copies
> as the backend).
> 
>                          Baseline   Deferred Release
> Interhost receive to VM   7.2 Gb/s  ~9 Gbit/s
> Interhost aggregate      24 Gb/s    28 Gb/s
> Intrahost single stream  14 Gb/s    14 Gb/s
> Intrahost aggregate      34 Gb/s    36 Gb/s
> Aggregate disk write    900 MB/s   900 MB/s
> Aggregate disk read     890 MB/s   890 MB/s
> 
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>

Reviewed-by: Tim Deegan <tim@xxxxxxx>

Though if you're doing a v3...

>      for ( i = 0; i < count; i++ )
>      {
>          if (i && hypercall_preempt_check())

while you're here, you could add the missing spaces to this if ( ).

Cheers,

Tim.

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