On Thu, Apr 02, 2015 at 04:23:18PM +0200, Mateusz Guzik wrote: M> Well, a thread migrating to another cpu is the standard thing everyone M> sees.
How often do you see it right in a particular window of 2 or 3 instructions? If you carefully read the thread I referred to, you would notice that on many arches, save amd64 and i386, all systems stats are prone to mangling the stats due to migration within PCPU_INC. Look here: grep '^#define PCPU_ADD' sys/*/include/pcpu.h Do we have reports on not precise enough statistics, yet? M> I don't feel that strongly about changing the code. If it stays as it M> is, it definitely needs the comment I mentioned explaining why migration M> is fine. I just added the comment. M> If the code was to be changed a machdep counter_u64_fetchadd seems like M> the only course of action. If we have more places in kernel, where such API is required, I would do it. Alas, seems like not possible to make it without critical section, even on amd64. Note that counter_u64_add() on amd64 is critical-less. -- Totus tuus, Glebius. _______________________________________________ svn-src-head@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
