Nathan Lynch <[email protected]> wrote:
>
> Eric Dumazet wrote:
> >
> > [PATCH] HOTPLUG_CPU : avoid hitting too many cachelines in recalc_bh_state()
> >
> > Instead of using for_each_cpu(i), we can use for_each_online_cpu(i) : The
> > difference matters if HOTPUG_CPU=y
> >
> > When a CPU goes offline (ie removed from online map), it might have a non
> > null bh_accounting.nr, so this patch adds a transfert of this counter to an
> > online CPU counter.
> >
> > We already have a hotcpu_notifier, (function buffer_cpu_notify()), where we
> > can do this bh_accounting.nr transfert.
> >
> > Signed-off-by: Eric Dumazet <[email protected]>
>
> > --- a/fs/buffer.c 2006-02-10 15:08:21.000000000 +0100
> > +++ b/fs/buffer.c 2006-02-10 15:47:55.000000000 +0100
> > @@ -3138,7 +3138,7 @@
> > if (__get_cpu_var(bh_accounting).ratelimit++ < 4096)
> > return;
> > __get_cpu_var(bh_accounting).ratelimit = 0;
> > - for_each_cpu(i)
> > + for_each_online_cpu(i)
> > tot += per_cpu(bh_accounting, i).nr;
> > buffer_heads_over_limit = (tot > max_buffer_heads);
> > }
> > @@ -3187,6 +3187,9 @@
> > brelse(b->bhs[i]);
> > b->bhs[i] = NULL;
> > }
> > + get_cpu_var(bh_accounting).nr += per_cpu(bh_accounting, cpu).nr ;
> > + per_cpu(bh_accounting, cpu).nr = 0;
> > + put_cpu_var(bh_accounting);
> > }
>
> But now there is a window between the time the cpu is marked offline
> and the time its bh_accounting.nr is moved to another cpu. So
> recalc_bh_state could fail to set buffer_heads_over_limit when it
> should.
Yes, there is a wee race there, but the consequences of a glitch or small
inaccuracy in buffer_heads_over_limit will be transient and negligibe.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
