Messages in this thread | | | Date | Thu, 9 Apr 2015 09:09:17 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] hrtimer: Replace cpu_base->active_bases with a direct check of the active list |
| |
* Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, Apr 09, 2015 at 08:28:41AM +0200, Ingo Molnar wrote: > > Btw., does cpu_base->active_bases even make sense? hrtimer bases are > > fundamentally percpu, and to check whether there are any pending > > timers is a very simple check: > > > > base->active->next != NULL > > > > Yeah, that's 3 pointer dereferences from cpu_base, iow you traded a > single bit test on an already loaded word for 3 potential cacheline > misses.
But the clock bases are not aligned to cachelines, and we have 4 of them. So in practice when we access one, we'll load the next one anyway.
Furthermore the simplification is measurable, and a fair bit of it is in various fast paths. I'd rather trade a bit of a cacheline footprint for less overall complexity and faster code.
Thanks,
Ingo
| |