From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754167Ab2ATP7c (ORCPT ); Fri, 20 Jan 2012 10:59:32 -0500 Received: from mail-ww0-f44.google.com ([74.125.82.44]:63610 "EHLO mail-ww0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753732Ab2ATP72 (ORCPT ); Fri, 20 Jan 2012 10:59:28 -0500 Message-ID: <1327075164.12389.31.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC> Subject: [PATCH] proc: speedup /proc/stat handling From: Eric Dumazet To: Andrew Morton Cc: KAMEZAWA Hiroyuki , Glauber Costa , Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, Russell King - ARM Linux , Paul Tuner Date: Fri, 20 Jan 2012 16:59:24 +0100 Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.1- Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On a typical 16 cpus machine, "cat /proc/stat" gives more than 4096 bytes, and is slow : # strace -T -o /tmp/STRACE cat /proc/stat | wc -c 5826 # grep "cpu " /tmp/STRACE read(0, "cpu 1949310 19 2144714 12117253"..., 32768) = 5826 <0.001504> Thats partly because show_stat() must be called twice since initial buffer size is too small (4096 bytes for less than 32 possible cpus) Fix this by : 1) Taking into account nr_irqs in the initial buffer sizing. 2) Using ksize() to allow better filling of initial buffer. 3) Reduce the bloat on "intr ..." line : Dont output trailing " 0" values at the end of irq range. An alternative to 1) would be to remember the largest m->count reached in show_stat() Signed-off-by: Eric Dumazet Cc: Glauber Costa Cc: Russell King - ARM Linux Cc: KAMEZAWA Hiroyuki Cc: Andrew Morton Cc: Paul Tuner Cc: Peter Zijlstra Cc: Ingo Molnar --- fs/proc/stat.c | 33 +++++++++++++++++++++++++-------- 1 file changed, 25 insertions(+), 8 deletions(-) diff --git a/fs/proc/stat.c b/fs/proc/stat.c index 121f77c..78db0fa 100644 --- a/fs/proc/stat.c +++ b/fs/proc/stat.c @@ -49,6 +49,20 @@ static u64 get_iowait_time(int cpu) return iowait; } +/* + * Most irqs at the end of the range are never used. + * Find the upper limit, to not output trailing " 0" values + */ +static int highest_irq_used(void) +{ + int nr; + + for (nr = nr_irqs; nr; nr--) + if (kstat_irqs(nr - 1)) + break; + return nr; +} + static int show_stat(struct seq_file *p, void *v) { int i, j; @@ -129,10 +143,10 @@ static int show_stat(struct seq_file *p, void *v) (unsigned long long)cputime64_to_clock_t(guest_nice)); } seq_printf(p, "intr %llu", (unsigned long long)sum); - - /* sum again ? it could be updated? */ - for_each_irq_nr(j) - seq_printf(p, " %u", kstat_irqs(j)); + /* Note that the "sum" value can already be obsolete. */ + j = highest_irq_used(); + for (i = 0; i < j; i++) + seq_printf(p, " %u", kstat_irqs(i)); seq_printf(p, "\nctxt %llu\n" @@ -157,14 +171,17 @@ static int show_stat(struct seq_file *p, void *v) static int stat_open(struct inode *inode, struct file *file) { - unsigned size = 4096 * (1 + num_possible_cpus() / 32); + unsigned size = 1024 + 128 * num_possible_cpus(); char *buf; struct seq_file *m; int res; + /* minimum size to display a 0 count per interrupt : 2 bytes */ + size += 2 * nr_irqs; + /* don't ask for more than the kmalloc() max size */ - if (size > KMALLOC_MAX_SIZE) - size = KMALLOC_MAX_SIZE; + size = min_t(unsigned, size, KMALLOC_MAX_SIZE); + buf = kmalloc(size, GFP_KERNEL); if (!buf) return -ENOMEM; @@ -173,7 +190,7 @@ static int stat_open(struct inode *inode, struct file *file) if (!res) { m = file->private_data; m->buf = buf; - m->size = size; + m->size = ksize(buf); } else kfree(buf); return res;