MIME-Version: 1.0
In-Reply-To: <alpine.DEB.2.00.1008301114460.10316@router.home>
References: <1281374816-904-1-git-send-email-ngupta@vflare.org>
	<1281374816-904-4-git-send-email-ngupta@vflare.org>
	<alpine.DEB.2.00.1008301114460.10316@router.home>
Date: Tue, 31 Aug 2010 16:31:08 -0400
Message-ID: <AANLkTikdhnr12uU8Wp60BygZwH770RBfxyfLNMzUsQje@mail.gmail.com>
Subject: Re: [PATCH 03/10] Use percpu stats
From: Nitin Gupta <ngupta@vflare.org>
To: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>, Minchan Kim <minchan.kim@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>, Greg KH <greg@kroah.com>,
        Linux Driver Project <devel@driverdev.osuosl.org>,
        linux-mm <linux-mm@kvack.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8BIT
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1299
Lines: 39

On Mon, Aug 30, 2010 at 12:20 PM, Christoph Lameter <cl@linux.com> wrote:
> On Mon, 9 Aug 2010, Nitin Gupta wrote:
>
>> -static void zram_stat_inc(u32 *v)
>> +static void zram_add_stat(struct zram *zram,
>> + ? ? ? ? ? ? ? ? ? ? enum zram_stats_index idx, s64 val)
>> ?{
>> - ? ? *v = *v + 1;
>> + ? ? struct zram_stats_cpu *stats;
>> +
>> + ? ? preempt_disable();
>> + ? ? stats = __this_cpu_ptr(zram->stats);
>> + ? ? u64_stats_update_begin(&stats->syncp);
>> + ? ? stats->count[idx] += val;
>> + ? ? u64_stats_update_end(&stats->syncp);
>> + ? ? preempt_enable();
>
> Maybe do
>
> #define zram_add_stat(zram, index, val)
> ? ? ? ? ? ? ? ?this_cpu_add(zram->stats->count[index], val)
>
> instead? It creates an add in a single "atomic" per cpu instruction and
> deals with the fallback scenarios for processors that cannot handle 64
> bit adds.
>
>

Yes, this_cpu_add() seems sufficient. I can't recall why I used u64_stats_*
but if it's not required for atomic access to 64-bit then why was it added to
the mainline in the first place?

Thanks,
Nitin
--
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/