linux-kernel - Re: [PATCH] sched/core: expand sched_getaffinity(2) to return number of CPUs

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Message-ID: <20190405110415.GP12232@hirez.programming.kicks-ass.net>
Date:   Fri, 5 Apr 2019 13:04:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Florian Weimer <fweimer@...hat.com>
Cc:     Alexey Dobriyan <adobriyan@...il.com>, mingo@...hat.com,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [PATCH] sched/core: expand sched_getaffinity(2) to return number
 of CPUs

On Fri, Apr 05, 2019 at 12:16:39PM +0200, Florian Weimer wrote:

> > True; but I suppose glibc already does lots of that anyway, right? It
> > does contain the right information.
> 
> If I recall correctly my last investigation,
> /sys/devices/system/cpu/possible does not reflect the size of the
> affinity mask, either.

Strictly speaking correct; the bitmap can be longer than the highest
possible cpu number, however the remainder would be 0-padding and could
thus be stripped without issue.

So a bitmap sized to fit the max possible cpu number, should for all
practical purposes suffice.