2012/8/15 Jianpeng Ma <majianpeng@xxxxxxxxx>:
> On 2012-08-15 11:51 Shaohua Li <shli@xxxxxxxxxx> Wrote:
>>2012/8/14 Jianpeng Ma <majianpeng@xxxxxxxxx>:
>>> On 2012-08-13 10:20 Shaohua Li <shli@xxxxxxxxxx> Wrote:
>>>>2012/8/13 Shaohua Li <shli@xxxxxxxxxx>:
>>>>> On Mon, Aug 13, 2012 at 09:06:45AM +0800, Jianpeng Ma wrote:
>>>>>> On 2012-08-13 08:21 Shaohua Li <shli@xxxxxxxxxx> Wrote:
>>>>>> >2012/8/11 Jianpeng Ma <majianpeng@xxxxxxxxx>:
>>>>>> >> On 2012-08-09 16:58 Shaohua Li <shli@xxxxxxxxxx> 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
>>>>>> >
>>>>>> >some sysfs entries print out '\n', some not, I don't mind add it
>>>>>> I search kernel code found places which like this print out '\n';
>>>>>> Can you tell rule which use or not?
>>>>>> Thanks!
>>>>>
>>>>> I'm not aware any rule about this
>>>>>
>>>>>> >> 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.
>>>>>> >
>>>>>> >So multiple threads handle stripes reduce request merge. In your
>>>>>> >workload, raid5d isn't a bottleneck at all. In practice, I thought only
>>>>>> >array which can drive high IOPS needs enable multi thread. And
>>>>>> >if you create multiple threads, better let the threads handle different
>>>>>> >cpus.
>>>>>> I will test for multiple threads.
>>>>> Thanks
>>> I used fio for randwrite test using four thread which run different cpus.
>>> The bs is 4k/8k/16k.
>>> The result isn't increase regardless of whether using authread(four authread which run different cpu) or not?
>>> Maybe my test config had problem?
>>
>>how fast is your raid? If your raid can't drive high IOPS, it's
>>not strange multithread makes no difference.
>>
> Only 175 for 4K. I think your patch for harddisk dose not effect.
> Maybe it's only for ssd.
>>>>BTW, can you try below patch for the above dd workload?
>>>>http://git.kernel.dk/?p=linux-block.git;a=commitdiff;h=274193224cdabd687d804a26e0150bb20f2dd52c
>>>>That one is reverted in upstream, but eventually we should make it
>>>>enter again after some CFQ issues are fixed.
>>> I tested this patch.And not found problem.And the performance did not increase.
>>
>>Ok, each thread delivers request in random time, so merge doesn't
>>work even with that patch. I didn't worry about big size request too
>>much, since if you set correct affinity for the auxthread, the issue
>>should go away. And mulithread is for fast storage, I suppose it has
>>no advantages for harddisk raid. On the other hand, maybe we can
>>make MAX_STRIPE_BATCH bigger. Currently it's 8, so the auxthread
>>will dispatch 8*4k request for the workload. Changing it to 16
>>(16*4=64k) should be good enough even for hard disk raid.
>>
> I review your code and have a question about wakeup authread:
>>static void raid5_wakeup_stripe_thread(struct stripe_head *sh)
>>{
>> struct r5conf *conf = sh->raid_conf;
>> struct raid5_percpu *percpu;
>> int i, orphaned = 1;
>>
>> percpu = per_cpu_ptr(conf->percpu, sh->cpu);
>> for_each_cpu(i, &percpu->handle_threads) {
>> md_wakeup_thread(conf->aux_threads[i]->thread);
>> orphaned = 0;
>> }
> If there are small stripes in handle_threads of cpu0.But the authread0/1 can run cpu0.
> It's no necessary to wakup all thread.authread0 may exec all stripe,but the authread1 only wakeup and sleep,but it will spin_lock_irq(&conf->device_lock).
> I think you should add some limited to do .
I used to have a counter for stripes queued, with it, we can determine
how many threads should be waken up. That is what I did when each
each thread can handle stripes from any CPU. I thought this problem
isn't sever now since each thread can just handle strips from one or
several CPUs. If this really is a problem, we can fix it later, but my test
doesn't show this is a problem.
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