Messages in this thread | | | Date | Thu, 2 Feb 2012 13:00:21 -0800 | Subject | Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v5 | From | Venki Pallipadi <> |
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On Thu, Feb 2, 2012 at 12:19 PM, Andrew Morton <akpm@linux-foundation.org> wrote: > On Fri, 03 Feb 2012 06:33:02 +1030 > Rusty Russell <rusty@rustcorp.com.au> wrote: > >> On Wed, 1 Feb 2012 14:01:25 -0800, Andrew Morton <akpm@linux-foundation.org> wrote: >> > > Though most of the callers of these two routines are init time (with few >> > > exceptions of runtime calls), it is cleaner to use variables >> > > and not go through this repeated mask based calculation. >> > >> > Looks good to me. >> >> But, I wonder who's asking num_possible_cpus(). It's not a very useful >> thing to know, though some arch's "know" it's contiguous, so can cheat. >> >> Optimizing it seems particularly foolish. > > We're fools for optimisations! >
I would think that if we are giving an API people will abuse it sooner or later :-).
>> We either audit and wean >> everyone off who's using it incorrectly, or insist on contiguous CPU >> numbers and drop the mask altogether. > > drivers/block/nvme.c looks like it's assuming a contiguous map. Maybe > also drivers/scsi/bnx2fc (wtf?). I didn't see anything else outside > arch code. >
Yes. I found a bunch of them which seemed obviously wrong. Doing things like allocating space based on num_possible_cpus() and accessing the space with get_cpu() or doing cou_online() check etc.
arch/x86/kernel/apic/x2apic_uv_x.c arch/x86/kernel/cpu/mcheck/mce-inject.c arch/x86/platform/uv/tlb_uv.c drivers/scsi/bnx2fc/bnx2fc_io.c kernel/debug/kdb/kdb_bt.c
I have a patch to fix these obvious ones. But, there are other users which were not very obvious to me and also I am know of code in older kernels (code which since have been rewritten) which can get benefit of this API change.
Thanks, Venki -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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