From: Pete Zaitcev <zaitcev@redhat.com>
To: James Bottomley <James.Bottomley@SteelEye.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Optimisation for smp_num_cpus loop in hotplug
Date: Fri, 21 Jun 2002 00:16:18 -0400 [thread overview]
Message-ID: <200206210416.g5L4GIx16142@devserv.devel.redhat.com> (raw)
In-Reply-To: <mailman.1024617156.25656.linux-kernel2news@redhat.com>
> for (i = 0; i < NR_CPUS; i++) {
> if (!cpu_online(i))
> continue;
>
> Since the cpu online map is probably going to be quite sparse,
> could I suggest this alternative, which doesn't have to loop 32 times:
> +#define for_each_cpu(cpu, mask) \
> + for(mask = cpu_online_map; \
> + cpu = __ffs(mask), mask != 0; \
> + mask &= ~(1<<cpu))
> +
This is neat, but I'd like to see it work with O(1) as well.
Mingo's code uses some long bitmaps.
-- Pete
next parent reply other threads:[~2002-06-21 4:16 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.1024617156.25656.linux-kernel2news@redhat.com>
2002-06-21 4:16 ` Pete Zaitcev [this message]
2002-06-21 13:10 ` Optimisation for smp_num_cpus loop in hotplug James Bottomley
2002-06-20 23:41 James Bottomley
2002-06-21 15:14 ` Rusty Russell
2002-06-21 15:31 ` James Bottomley
2002-06-21 19:17 ` Rusty Russell
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