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 <tipbot@xxxxxxxxx> 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.
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