On 09/16/2013 01:07 AM, Peter Zijlstra wrote:
On Fri, Sep 13, 2013 at 11:18:21PM -0700, Andi Kleen wrote:
tip-bot for Peter Zijlstra <tip...@zytor.com> writes:
+
+ at = (struct pebs_record_nhm *)(unsigned long)ds->pebs_buffer_base;
+ top = (struct pebs_record_nhm *)(unsigned long)ds->pebs_index;
ds->pebs_index = ds->pebs_buffer_base;
+ n = (top - at) / x86_pmu.pebs_record_size;
This adds a full slow division to the PEBS hot path.
Does not seem like a improvement to me.
There already was an implicit division there, and
sizeof(pebs_record_hsw) = 176, can it really optimize that constant
division?
gcc can optimize ANY constant division, if nothing else then by
reciprocal multiplication.
-hpa
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