Re: [patch 2/2 v3]raid5: create multiple threads to handle stripes

["Jianpeng Ma" <majianpeng@gmail.com>]

On 2012-08-09 16:58 Shaohua Li <shli@kernel.org> Wrote:
>This is a new tempt to make raid5 handle stripes in multiple threads, as
>suggested by Neil to have maxium flexibility and better numa binding. It
>basically is a combination of my first and second generation patches. By
>default, no multiple thread is enabled (all stripes are handled by raid5d).
>
>An example to enable multiple threads:
>#echo 3 > /sys/block/md0/md/auxthread_number
>This will create 3 auxiliary threads to handle stripes. The threads can run
>on any cpus and handle stripes produced by any cpus.
>
>#echo 1-3 > /sys/block/md0/md/auxth0/cpulist
>This will bind auxiliary thread 0 to cpu 1-3, and this thread will only handle
>stripes produced by cpu 1-3. User tool can further change the thread's
>affinity, but the thread can only handle stripes produced by cpu 1-3 till the
>sysfs entry is changed again.
>
>If stripes produced by a CPU aren't handled by any auxiliary thread, such
>stripes will be handled by raid5d. Otherwise, raid5d doesn't handle any
>stripes.
>
I tested and found two problem(maybe not).

1:print cpulist of auxth, you maybe lost print the '\n'.
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 7c8151a..3700cdc 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4911,9 +4911,13 @@ struct raid5_auxth_sysfs {
 static ssize_t raid5_show_thread_cpulist(struct mddev *mddev,
        struct raid5_auxth *thread, char *page)
 {
+       int n;
        if (!mddev->private)
                return 0;
-       return cpulist_scnprintf(page, PAGE_SIZE, &thread->work_mask);
+       n = cpulist_scnprintf(page, PAGE_SIZE - 2, &thread->work_mask);
+       page[n++] = '\n';
+       page[n] = 0;
+       return n;
 }
 
 static ssize_t

2: Test 'dd if=/dev/zero of=/dev/md0 bs=2M ', the performance regress remarkable.
auxthread_number=0, 200MB/s;
auxthread_number=4, 95MB/s.