Date: Sun, 11 Jul 2010 10:27:03 +0100 From: "Robert N. M. Watson" <rwatson@freebsd.org> To: Gabor PALI <pgj@FreeBSD.org> Cc: svn-src-head@freebsd.org Subject: Re: svn commit: r209119 - head/sys/sys Message-ID: <001126CD-F68F-46A3-90CE-CA2BE6E36B8E@freebsd.org> In-Reply-To: <AANLkTikkDxOPhiA_NYmwO_Bpxb9g2M7UGRpBW85dBN_I@mail.gmail.com> References: <4C376B0E.9050505@FreeBSD.org> <alpine.BSF.2.00.1007091949170.94277@fledge.watson.org> <4C37713D.5060202@FreeBSD.org> <4A28A601-C87F-47C6-8CBE-5F1BF866CA4A@FreeBSD.org> <AANLkTikkDxOPhiA_NYmwO_Bpxb9g2M7UGRpBW85dBN_I@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On 11 Jul 2010, at 04:18, Gabor PALI wrote: > On Sat, Jul 10, 2010 at 5:24 PM, Robert N. M. Watson > <rwatson@freebsd.org> wrote: >> If we can do it in one atomic in the common case, and two atomics in = an edge case, that sounds fine. I think any use of locking(9) would be = sufficiently costly as to not be worth the improvements in consistency, = given the frequency of statistics operations. >=20 > I have tried to use atomic operations for counting (without > locking(9)), but they turned out to be significantly slower than the > naive case indeed. If consistency is not so important for statistics, > whether would it be safe to simply use 64-bit variables for counters > everywhere on all architectures? I think the worry comes down to: an occasional missed packet is OK, but = a duplicated carry(for example) from the lower 32 bits to the upper 32 = bits would put the counter off by 4 billion, which is not really = acceptable. What sort of measurement did you do to show the speed loss, BTW? Robert
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?001126CD-F68F-46A3-90CE-CA2BE6E36B8E>