linux-kernel - Re: [RFC PATCH 0/6] Convert all tasklets to workqueues

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Message-ID: <e9c3a7c20706281102l5db2e91alf465e7983d68f284@mail.gmail.com>
Date:	Thu, 28 Jun 2007 11:02:53 -0700
From:	"Dan Williams" <dan.j.williams@...el.com>
To:	"Steven Rostedt" <rostedt@...dmis.org>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Christoph Hellwig" <hch@...radead.org>,
	"john stultz" <johnstul@...ibm.com>,
	"Oleg Nesterov" <oleg@...sign.ru>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Dipankar Sarma" <dipankar@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>, kuznet@....inr.ac.ru,
	"Jeff Garzik" <jeff@...zik.org>
Subject: Re: [RFC PATCH 0/6] Convert all tasklets to workqueues

On 6/28/07, Steven Rostedt <rostedt@...dmis.org> wrote:
>
> Hi Dan,
>
> On Mon, 25 Jun 2007, Dan Williams wrote:
>
> > Yes you are right, ARM does not flush L1 when prev==next in switch_mm.
> >
> > > Perhaps something else is at fault here.
> > >
> > I'll try and dig a bit deeper...
>
> BTW:
>
>  static int __init iop_adma_init (void)
>  {
> +       iop_adma_workqueue = create_workqueue("iop-adma");
> +       if (!iop_adma_workqueue)
> +               return -ENODEV;
> +
>
> Could you also try upping the prio of all the "iop-adma" threads?
>
Unfortunately setting the thread to real time priority makes
throughput slightly worse.  Instead of floating around 35MB/s the
resync speed is stuck around 30MB/s:

[ iop-adma: hi-prio workqueue based callbacks ]
iq81340mc:~# cat /proc/mdstat
Personalities : [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
md0 : active raid5 sdd[4] sdc[2] sdb[1] sda[0]
      468872448 blocks level 5, 64k chunk, algorithm 2 [4/3] [UUU_]
      [>....................]  recovery =  3.9% (6107424/156290816)
finish=84.9min speed=29448K/sec

The iop-adma tasklet cleans up any completed descriptors and in the
process calls any attached callbacks.  For the raid5 resync case the
callback is simply:

static void ops_complete_check(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;
        int pd_idx = sh->pd_idx;

        pr_debug("%s: stripe %llu\n", __FUNCTION__,
                (unsigned long long)sh->sector);

        if (test_and_clear_bit(STRIPE_OP_MOD_DMA_CHECK, &sh->ops.pending) &&
                sh->ops.zero_sum_result == 0)
                set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);

        set_bit(STRIPE_OP_CHECK, &sh->ops.complete);
        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}


[ iop-adma: tasklet based callbacks ]
iq81340mc:~# cat /proc/mdstat
Personalities : [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
md0 : active raid5 sdd[4] sdc[2] sdb[1] sda[0]
      468872448 blocks level 5, 64k chunk, algorithm 2 [4/3] [UUU_]
      [=>...................]  recovery =  5.1% (8024248/156290816)
finish=47.9min speed=51486K/sec

--
Dan
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