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Date: Thu, 28 Feb 2013 18:25:26 +0900
From: Namhyung Kim <namhyung@...nel.org>
To: Michael Wang <wangyun@...ux.vnet.ibm.com>
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 Michael,
On Thu, 28 Feb 2013 14:38:03 +0800, Michael Wang wrote:
> wake_affine() stuff is trying to bind related tasks closely, but it doesn't
> work well according to the test on 'perf bench sched pipe' (thanks to Peter).
>
> Besides, pgbench show that blindly using wake_affine() will eat a lot of
> performance.
>
> Thus, we need a new solution, it should detect the tasks related to each
> other, bind them closely, take care the balance, latency and performance
> at the same time.
>
> Feature wakeup buddy seems like a good solution (thanks to Mike for the hint).
>
> The feature introduced waker, wakee pointer and their ref count, along with
> the new knob sysctl_sched_wakeup_buddy_ref.
>
> Now in select_task_rq_fair(), when current (task B) try to wakeup p (task A),
> if match:
>
> 1. A->waker == B && A->wakee == B
> 2. A->waker_ref > sysctl_sched_wakeup_buddy_ref
> 3. A->wakee_ref > sysctl_sched_wakeup_buddy_ref
>
> then A is the wakeup buddy of B, which means A and B is likely to utilize
> the memory of each other.
>
> 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 ;-)
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.
> +
> +/*
> + * 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?
> 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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