On Tue, May 19, 2015 at 05:27:10PM +0200, Michal Hocko wrote: > On Tue 19-05-15 16:13:02, Mel Gorman wrote: > [...] > > :ffffffff811c160f: je ffffffff811c1630 <mem_cgroup_try_charge+0x40> > > :ffffffff811c1611: xor %eax,%eax > > :ffffffff811c1613: xor %ebx,%ebx > > 1 1.7e-05 :ffffffff811c1615: mov %rbx,(%r12) > > 7 1.2e-04 :ffffffff811c1619: add $0x10,%rsp > > 1211 0.0203 :ffffffff811c161d: pop %rbx > > 5 8.4e-05 :ffffffff811c161e: pop %r12 > > 5 8.4e-05 :ffffffff811c1620: pop %r13 > > 1249 0.0210 :ffffffff811c1622: pop %r14 > > 7 1.2e-04 :ffffffff811c1624: pop %rbp > > 5 8.4e-05 :ffffffff811c1625: retq > > :ffffffff811c1626: nopw %cs:0x0(%rax,%rax,1) > > 295 0.0050 :ffffffff811c1630: mov (%rdi),%rax > > 160703 2.6973 :ffffffff811c1633: mov %edx,%r13d > > Huh, what? Even if this was off by one and the preceding instruction has > consumed the time. This would be reading from page->flags but the page > should be hot by the time we got here, no? > I would have expected so but it's not the first time I've seen cases where examining the flags was a costly instruction. I suspect it's due to an ordering issue or more likely, a frequent branch mispredict that is being accounted for against this instruction. -- Mel Gorman SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
