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SubjectRe: [PATCH 5/5] mm: x86: Revisit tlb_flushall_shift tuning for page flushes except on IvyBridge
On 01/09/2014 09:34 AM, Mel Gorman wrote:
> There was a large ebizzy performance regression that was bisected to commit
> 611ae8e3 (x86/tlb: enable tlb flush range support for x86). The problem
> was related to the tlb_flushall_shift tuning for IvyBridge which was
> altered. The problem is that it is not clear if the tuning values for each
> CPU family is correct as the methodology used to tune the values is unclear.
>
> This patch uses a conservative tlb_flushall_shift value for all CPU families
> except IvyBridge so the decision can be revisited if any regression is found
> as a result of this change. IvyBridge is an exception as testing with one
> methodology determined that the value of 2 is acceptable. Details are in the
> changelog for the patch "x86: mm: Change tlb_flushall_shift for IvyBridge".
>
> One important aspect of this to watch out for is Xen. The original commit
> log mentioned large performance gains on Xen. It's possible Xen is more
> sensitive to this value if it flushes small ranges of pages more frequently
> than workloads on bare metal typically do.
>
> Signed-off-by: Mel Gorman <mgorman@suse.de>

Reviewed-by: Rik van Riel <riel@redhat.com>



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