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Date: Fri, 01 Mar 2013 10:18:50 +0800
From: Michael Wang <wangyun@...ux.vnet.ibm.com>
To: Namhyung Kim <namhyung@...nel.org>
CC: LKML <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Mike Galbraith <efault@....de>, Paul Turner <pjt@...gle.com>,
Alex Shi <alex.shi@...el.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Ram Pai <linuxram@...ibm.com>,
"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH] sched: wakeup buddy
Hi, Namhyung
Thanks for your reply.
On 02/28/2013 05:25 PM, Namhyung Kim wrote:
[snip]
>> Thus, if B is also the wakeup buddy of A, which means no other task has
>> destroyed their relationship, then A is likely to benefit from the cached
>> data of B, make them running closely is likely to gain benefit.
>
> Not sure if it should require bidirectional relationship. Looks like
> just for benchmarks. Isn't there a one-way relationship that could get
> a benefit from this? I don't know ;-)
That's one point :)
Actually I have tried the one-way case at very beginning, the
performance is not good.
I think it was caused by that if A lost interesting on B and walking
with C, then make A and B closely won't gain so many benefit, since the
cached data of A is likely to benefit C not B now.
>
> Few nitpicks below..
>
>>
>> This patch add the feature wakeup buddy, reorganized the logical of
>> wake_affine() stuff with the new feature, by doing these, pgbench and
>> 'perf bench sched pipe' perform better.
>>
>> Highlight:
>> Default value of sysctl_sched_wakeup_buddy_ref is 8 temporarily,
>> please let me know if some number perform better on your system,
>> I'd like to make it bigger to make the decision more carefully,
>> so we could provide the solution when it is really needed.
>>
>> Comments are very welcomed.
>>
>> Test:
>> Test with a 12 cpu X86 server and tip 3.8.0-rc7.
>>
>> 'perf bench sched pipe' show nearly double improvement.
>>
>> pgbench result:
>> prev post
>>
>> | db_size | clients | tps | | tps |
>> +---------+---------+-------+ +-------+
>> | 22 MB | 1 | 10794 | | 10820 |
>> | 22 MB | 2 | 21567 | | 21915 |
>> | 22 MB | 4 | 41621 | | 42766 |
>> | 22 MB | 8 | 53883 | | 60511 | +12.30%
>> | 22 MB | 12 | 50818 | | 57129 | +12.42%
>> | 22 MB | 16 | 50463 | | 59345 | +17.60%
>> | 22 MB | 24 | 46698 | | 63787 | +36.59%
>> | 22 MB | 32 | 43404 | | 62643 | +44.33%
>>
>> | 7484 MB | 1 | 7974 | | 8014 |
>> | 7484 MB | 2 | 19341 | | 19534 |
>> | 7484 MB | 4 | 36808 | | 38092 |
>> | 7484 MB | 8 | 47821 | | 51968 | +8.67%
>> | 7484 MB | 12 | 45913 | | 52284 | +13.88%
>> | 7484 MB | 16 | 46478 | | 54418 | +17.08%
>> | 7484 MB | 24 | 42793 | | 56375 | +31.74%
>> | 7484 MB | 32 | 36329 | | 55783 | +53.55%
>>
>> | 15 GB | 1 | 7636 | | 7880 |
>> | 15 GB | 2 | 19195 | | 19477 |
>> | 15 GB | 4 | 35975 | | 37962 |
>> | 15 GB | 8 | 47919 | | 51558 | +7.59%
>> | 15 GB | 12 | 45397 | | 51163 | +12.70%
>> | 15 GB | 16 | 45926 | | 53912 | +17.39%
>> | 15 GB | 24 | 42184 | | 55343 | +31.19%
>> | 15 GB | 32 | 35983 | | 55358 | +53.84%
>>
>> Signed-off-by: Michael Wang <wangyun@...ux.vnet.ibm.com>
>> ---
> [SNIP]
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 81fa536..d5acfd8 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -3173,6 +3173,75 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
>> }
>>
>> /*
>> + * Reduce sysctl_sched_wakeup_buddy_ref will reduce the preparation time
>> + * to active the wakeup buddy feature, and make it agile, however, this
>> + * will increase the risk of misidentify.
>> + *
>> + * Check wakeup_buddy() for the usage.
>> + */
>> +unsigned int sysctl_sched_wakeup_buddy_ref = 8UL;
>
> It seems that just 8U (or even 8) is enough.
I will correct it.
>
>> +
>> +/*
>> + * wakeup_buddy() help to check whether p1 is the wakeup buddy of p2.
>> + *
>> + * Return 1 for yes, 0 for no.
>> +*/
>> +static inline int wakeup_buddy(struct task_struct *p1, struct task_struct *p2)
>> +{
>> + if (p1->waker != p2 || p1->wakee != p2)
>> + return 0;
>> +
>> + if (p1->waker_ref < sysctl_sched_wakeup_buddy_ref)
>> + return 0;
>> +
>> + if (p1->wakee_ref < sysctl_sched_wakeup_buddy_ref)
>> + return 0;
>> +
>> + return 1;
>> +}
> [SNIP]
>> @@ -3399,6 +3490,8 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
>> unlock:
>> rcu_read_unlock();
>>
>> + wakeup_ref(p);
>> +
>
> Why did you call it here? Shouldn't it be on somewhere in the ttwu?
I'd like to put the changes closely, just another 'bad' habit ;-)
But you notified me that I should add a check on WAKEUP flag, will
correct it.
Regards,
Michael Wang
>
>
>> return new_cpu;
>> }
>>
>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>> index c88878d..6845d24 100644
>> --- a/kernel/sysctl.c
>> +++ b/kernel/sysctl.c
>> @@ -424,6 +424,16 @@ static struct ctl_table kern_table[] = {
>> .extra1 = &one,
>> },
>> #endif
>> +#ifdef CONFIG_SMP
>> + {
>> + .procname = "sched_wakeup_buddy_ref",
>> + .data = &sysctl_sched_wakeup_buddy_ref,
>> + .maxlen = sizeof(unsigned int),
>> + .mode = 0644,
>> + .proc_handler = proc_dointvec_minmax,
>> + .extra1 = &one,
>> + },
>> +#endif
>> #ifdef CONFIG_PROVE_LOCKING
>> {
>> .procname = "prove_locking",
> --
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