Hi, * Martin Bligh ([EMAIL PROTECTED]) wrote: > Christoph Lameter wrote: > >On Mon, 9 Jul 2007, Martin Bligh wrote: > > > >>Those numbers came from Mathieu Desnoyers (LTTng) if you > >>want more details. > > > >Okay the source for these numbers is in his paper for the OLS 2006: Volume > >1 page 208-209? I do not see the exact number that you referred to there. >
Hrm, the reference page number is wrong: it is in OLS 2006, Vol. 1 page 216 (section 4.5.2 Scalability). I originally pulled out the page number from my local paper copy. oops. > Nope, he was a direct co-author on the paper, was > working here, and measured it. > > >He seems to be comparing spinlock acquire / release vs. cmpxchg. So I > >guess you got your material from somewhere else? > > I ran a test specifically for this paper where I got this result comparing the local irq enable/disable to local cmpxchg. > >Also the cmpxchg used there is the lockless variant. cmpxchg 29 cycles w/o > >lock prefix and 112 with lock prefix. Yep, I volountarily used the variant without lock prefix because the data is per cpu and I disable preemption. > > > >I see you reference another paper by Desnoyers: > >http://tree.celinuxforum.org/CelfPubWiki/ELC2006Presentations?action=AttachFile&do=get&target=celf2006-desnoyers.pdf > > > >I do not see anything relevant there. Where did those numbers come from? > > > >The lockless cmpxchg is certainly an interesting idea. Certain for some > >platforms I could disable preempt and then do a lockless cmpxchg. > Yes, preempt disabling or, eventually, the new thread migration disabling I just proposed as an RFC on LKML. (that would make -rt people happier) > Mathieu, can you give some more details? Obviously the exact numbers > will vary by archicture, machine size, etc, but it's a good point > for discussion. > Sure, also note that the UP cmpxchg (see asm-$ARCH/local.h in 2.6.22) is faster on architectures like powerpc and MIPS where it is possible to remove some memory barriers. See 2.6.22 Documentation/local_ops.txt for a thorough discussion. Don't hesitate ping me if you have more questions. Regards, Mathieu -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
