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From: Omar Sandoval <osandov@osandov.com>
To: Jens Axboe <axboe@fb.com>
Cc: axboe@kernel.dk, linux-kernel@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org
Subject: Re: [PATCH 7/8] wbt: add general throttling mechanism
Date: Thu, 1 Sep 2016 11:05:23 -0700
Message-ID: <20160901180523.GA3280@vader.DHCP.thefacebook.com> (raw)
In-Reply-To: <1472663151-18560-8-git-send-email-axboe@fb.com>

On Wed, Aug 31, 2016 at 11:05:50AM -0600, Jens Axboe wrote:
> We can hook this up to the block layer, to help throttle buffered
> writes. Or NFS can tap into it, to accomplish the same.
> 
> wbt registers a few trace points that can be used to track what is
> happening in the system:
> 
> wbt_lat: 259:0: latency 2446318
> wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
>                wmean=518866, wmin=15522, wmax=5330353, wsamples=57
> wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
> 
> This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
> dumps the current read/write stats for that window, and wbt_step shows a
> step down event where we now scale back writes. Each trace includes the
> device, 259:0 in this case.
> 
> Signed-off-by: Jens Axboe <axboe@fb.com>
> ---
>  include/linux/wbt.h        | 118 +++++++++
>  include/trace/events/wbt.h | 122 ++++++++++
>  lib/Kconfig                |   4 +
>  lib/Makefile               |   1 +
>  lib/wbt.c                  | 587 +++++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 832 insertions(+)
>  create mode 100644 include/linux/wbt.h
>  create mode 100644 include/trace/events/wbt.h
>  create mode 100644 lib/wbt.c
> 

[snip]

> diff --git a/lib/Kconfig b/lib/Kconfig
> index d79909dc01ec..5a65a1f91889 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -550,4 +550,8 @@ config STACKDEPOT
>  	bool
>  	select STACKTRACE
>  
> +config WBT
> +	bool
> +	select SCALE_BITMAP

Looks like this snuck in from your experiments to get this to work on
top of scale_bitmap?

[snip]

> +void __wbt_done(struct rq_wb *rwb)
> +{
> +	int inflight, limit;
> +
> +	inflight = atomic_dec_return(&rwb->inflight);
> +
> +	/*
> +	 * wbt got disabled with IO in flight. Wake up any potential
> +	 * waiters, we don't have to do more than that.
> +	 */
> +	if (unlikely(!rwb_enabled(rwb))) {
> +		wake_up_all(&rwb->wait);
> +		return;
> +	}
> +
> +	/*
> +	 * If the device does write back caching, drop further down
> +	 * before we wake people up.
> +	 */
> +	if (rwb->wc && !atomic_read(&rwb->bdi->wb.dirty_sleeping))
> +		limit = 0;
> +	else
> +		limit = rwb->wb_normal;
> +
> +	/*
> +	 * Don't wake anyone up if we are above the normal limit.
> +	 */
> +	if (inflight && inflight >= limit)
> +		return;
> +
> +	if (waitqueue_active(&rwb->wait)) {
> +		int diff = limit - inflight;
> +
> +		if (!inflight || diff >= rwb->wb_background / 2)
> +			wake_up_nr(&rwb->wait, 1);

wake_up(&rwb->wait)?

-- 
Omar

  reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-31 17:05 [PATCHSET v6] Throttled background buffered writeback Jens Axboe
2016-08-31 17:05 ` [PATCH 1/8] block: add WRITE_BG Jens Axboe
2016-09-01  7:55   ` Johannes Thumshirn
2016-09-01  7:59     ` Johannes Thumshirn
2016-08-31 17:05 ` [PATCH 2/8] writeback: add wbc_to_write_flags() Jens Axboe
2016-08-31 23:32   ` Omar Sandoval
2016-09-01  3:54     ` Jens Axboe
2016-08-31 17:05 ` [PATCH 3/8] writeback: use WRITE_BG for kupdate and background writeback Jens Axboe
2016-08-31 17:05 ` [PATCH 4/8] writeback: track if we're sleeping on progress in balance_dirty_pages() Jens Axboe
2016-08-31 17:05 ` [PATCH 5/8] block: add code to track actual device queue depth Jens Axboe
2016-08-31 17:05 ` [PATCH 6/8] block: add scalable completion tracking of requests Jens Axboe
2016-08-31 17:05 ` [PATCH 7/8] wbt: add general throttling mechanism Jens Axboe
2016-09-01 18:05   ` Omar Sandoval [this message]
2016-09-01 18:51     ` Jens Axboe
2016-08-31 17:05 ` [PATCH 8/8] writeback: throttle buffered writeback Jens Axboe
  -- strict thread matches above, loose matches on Subject: below --
2016-09-07 14:46 [PATCH 0/8] Throttled background buffered writeback v7 Jens Axboe
2016-09-07 14:46 ` [PATCH 7/8] wbt: add general throttling mechanism Jens Axboe
2016-04-26 15:55 [PATCHSET v5] Make background writeback great again for the first time Jens Axboe
2016-04-26 15:55 ` [PATCH 7/8] wbt: add general throttling mechanism Jens Axboe
2016-04-27 12:06   ` xiakaixu
2016-04-27 15:21     ` Jens Axboe
2016-04-28  3:29       ` xiakaixu
2016-04-28 11:05   ` Jan Kara
2016-04-28 18:53     ` Jens Axboe
2016-04-28 19:03       ` Jens Axboe
2016-05-03  9:34       ` Jan Kara
2016-05-03 14:23         ` Jens Axboe
2016-05-03 15:22           ` Jan Kara
2016-05-03 15:32             ` Jens Axboe
2016-05-03 15:40         ` Jan Kara
2016-05-03 15:48           ` Jan Kara
2016-05-03 16:59             ` Jens Axboe
2016-05-03 18:14               ` Jens Axboe
2016-05-03 19:07                 ` Jens Axboe

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