proc: speed up /proc/stat handling
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. Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Cc: Glauber Costa <glommer@parallels.com> Cc: Russell King - ARM Linux <linux@arm.linux.org.uk> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Paul Turner <pjt@google.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Ingo Molnar <mingo@elte.hu> Cc: Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -157,11 +157,14 @@ static int show_stat(struct seq_file *p, void *v)
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static int stat_open(struct inode *inode, struct file *file)
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{
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unsigned size = 4096 * (1 + num_possible_cpus() / 32);
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unsigned size = 1024 + 128 * num_possible_cpus();
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char *buf;
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struct seq_file *m;
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int res;
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/* minimum size to display an interrupt count : 2 bytes */
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size += 2 * nr_irqs;
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/* don't ask for more than the kmalloc() max size */
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if (size > KMALLOC_MAX_SIZE)
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size = KMALLOC_MAX_SIZE;
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@ -173,7 +176,7 @@ static int stat_open(struct inode *inode, struct file *file)
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if (!res) {
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m = file->private_data;
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m->buf = buf;
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m->size = size;
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m->size = ksize(buf);
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} else
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kfree(buf);
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return res;
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