On Fri, Apr 24, 2015 at 7:17 PM, Denys Vlasenko <vda.li...@googlemail.com> wrote: > On Fri, Apr 24, 2015 at 10:50 PM, Andy Lutomirski <l...@amacapital.net> wrote: >> On Fri, Apr 24, 2015 at 1:46 PM, Denys Vlasenko >>>> This might be way more trouble than it's worth. >>> >>> Exactly my feeling. What are you trying to save? About four CPU >>> cycles of checking %ss != __KERNEL_DS on each switch_to? >>> That's not worth bothering about. Your last patch seems to be perfect. >> >> We'll have to do the write to ss almost every time an AMD CPU sleeps >> in a syscall. > > Why do you think so? > Scheduling from a syscall which decided to block won't require > writing to %ss, since in this case %ss isn't NULL. > > Writing to %ss will happen every time we schedule from an interrupt. > With timer interrupt every 1 ms it means scheduling at most ~1000 > times per second, if _every_ such interrupt causes task switch. > This is still not often enough to worry.
OK, you've convinced me. I still think it can happen much more than ~1k times per second due to hrtimers (see my test case) or things like page faults, but those are all slow paths. v2 coming. -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
