On Wed, Mar 30, 2011 at 03:41:09PM +0200, Avi Kivity wrote: > On 03/30/2011 03:36 PM, Gleb Natapov wrote: > >> > >> It's wierd. Do you get perf hits in the copying? > >> > >How can I check. The memcpy is inlined. > > > > perf annotate x86_emulate_instruction > > (newer perf allows you to get there interactively from 'perf report') > > >> Copying a couple of hot cache lines shouldn't take any measurable Ah, forgot about it: First one: 27.71 : 1179f: f3 a5 rep movsl %ds:(%rsi),%es:(%rdi) Second one: 32.68 : 11888: f3 a5 rep movsl %ds:(%rsi),%es:(%rdi) > >> time compared to a heavyweight exit. > >> > >The whole function takes only 1.5% CPU. Perf measures how much this > >function become faster and heavyweight exit is not part of the function. > > It's still relative to exit cost. If the total exit was 2 us, then > a 1% decrease in cost translates to 40 ns. > > (well, that's not unlikely for a 256 byte memcpy, but let's be sure). > > -- > error compiling committee.c: too many arguments to function -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
