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From: Ming Lei <ming.lei@redhat.com>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-block <linux-block@vger.kernel.org>,
	Jens Axboe <axboe@kernel.dk>,
	linux-mmc <linux-mmc@vger.kernel.org>,
	linux-mtd@lists.infradead.org,
	Johannes Thumshirn <jthumshirn@suse.de>,
	Christoph Hellwig <hch@lst.de>,
	Damien Le Moal <damien.lemoal@wdc.com>,
	Paolo Valente <paolo.valente@linaro.org>
Subject: Re: [PATCH] block: Flag elevators suitable for single queue
Date: Mon, 1 Jun 2020 19:58:18 +0800	[thread overview]
Message-ID: <20200601115818.GB1190838@T590> (raw)
In-Reply-To: <CACRpkdYL4-Z=kaS+RfniVr=Sn-yOf+=CKMJDsn=eTK3atmGohg@mail.gmail.com>

On Mon, Jun 01, 2020 at 01:36:54PM +0200, Linus Walleij wrote:
> On Mon, Jun 1, 2020 at 9:50 AM Ming Lei <ming.lei@redhat.com> wrote:
> > On Thu, May 28, 2020 at 10:10:03AM +0200, Linus Walleij wrote:
> > > The Kyber block scheduler is not suitable for single hardware
> > > queue devices, so add a new flag for single hardware queue
> > > devices and add that to the deadline and BFQ schedulers
> > > so the Kyber scheduler will not be selected for single queue
> > > devices.
> >
> > The above may not be true for some single hw queue high performance HBA(
> > such as megasas), which can get better performance from none, so it is
> > reasonable to get better performance from kyber, see 6ce3dd6eec11 ("blk-mq:
> > issue directly if hw queue isn't busy in case of 'none'"), and the
> > following link:
> >
> > https://lore.kernel.org/linux-block/20180710010331.27479-1-ming.lei@redhat.com/
> 
> I see, but isn't the case rather that none is preferred and kyber gives
> the same characteristics because it's not standing in the way
> as much?

Kyber has its own characteristic, such as fair read & write, better
IO merge. And the decision on scheduler isn't only related with device,
but also with workloads.

> 
> It looks like if we should add a special flag for these devices with
> very fast single queues so they can say "I prefer none", do you
> agree?

I am not sure if it is easy to add such flag, because it isn't only
related with HBA, but also with the attached disks.


Thanks,
Ming


WARNING: multiple messages have this Message-ID (diff)
From: Ming Lei <ming.lei@redhat.com>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Jens Axboe <axboe@kernel.dk>,
	Damien Le Moal <damien.lemoal@wdc.com>,
	Paolo Valente <paolo.valente@linaro.org>,
	linux-mmc <linux-mmc@vger.kernel.org>,
	linux-block <linux-block@vger.kernel.org>,
	linux-mtd@lists.infradead.org,
	Johannes Thumshirn <jthumshirn@suse.de>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH] block: Flag elevators suitable for single queue
Date: Mon, 1 Jun 2020 19:58:18 +0800	[thread overview]
Message-ID: <20200601115818.GB1190838@T590> (raw)
In-Reply-To: <CACRpkdYL4-Z=kaS+RfniVr=Sn-yOf+=CKMJDsn=eTK3atmGohg@mail.gmail.com>

On Mon, Jun 01, 2020 at 01:36:54PM +0200, Linus Walleij wrote:
> On Mon, Jun 1, 2020 at 9:50 AM Ming Lei <ming.lei@redhat.com> wrote:
> > On Thu, May 28, 2020 at 10:10:03AM +0200, Linus Walleij wrote:
> > > The Kyber block scheduler is not suitable for single hardware
> > > queue devices, so add a new flag for single hardware queue
> > > devices and add that to the deadline and BFQ schedulers
> > > so the Kyber scheduler will not be selected for single queue
> > > devices.
> >
> > The above may not be true for some single hw queue high performance HBA(
> > such as megasas), which can get better performance from none, so it is
> > reasonable to get better performance from kyber, see 6ce3dd6eec11 ("blk-mq:
> > issue directly if hw queue isn't busy in case of 'none'"), and the
> > following link:
> >
> > https://lore.kernel.org/linux-block/20180710010331.27479-1-ming.lei@redhat.com/
> 
> I see, but isn't the case rather that none is preferred and kyber gives
> the same characteristics because it's not standing in the way
> as much?

Kyber has its own characteristic, such as fair read & write, better
IO merge. And the decision on scheduler isn't only related with device,
but also with workloads.

> 
> It looks like if we should add a special flag for these devices with
> very fast single queues so they can say "I prefer none", do you
> agree?

I am not sure if it is easy to add such flag, because it isn't only
related with HBA, but also with the attached disks.


Thanks,
Ming


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http://lists.infradead.org/mailman/listinfo/linux-mtd/

  reply	other threads:[~2020-06-01 11:58 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-28  8:10 [PATCH] block: Flag elevators suitable for single queue Linus Walleij
2020-05-28  8:10 ` Linus Walleij
2020-05-28  8:26 ` Johannes Thumshirn
2020-05-28  8:26   ` Johannes Thumshirn
2020-05-28 11:59   ` Linus Walleij
2020-05-28 11:59     ` Linus Walleij
2020-06-01  7:49 ` Ming Lei
2020-06-01  7:49   ` Ming Lei
2020-06-01 11:36   ` Linus Walleij
2020-06-01 11:36     ` Linus Walleij
2020-06-01 11:58     ` Ming Lei [this message]
2020-06-01 11:58       ` Ming Lei
2020-06-01 12:53       ` Ulf Hansson
2020-06-01 12:53         ` Ulf Hansson
2020-06-01 23:37         ` Damien Le Moal
2020-06-01 23:37           ` Damien Le Moal
2020-06-01 23:45           ` Jens Axboe
2020-06-01 23:45             ` Jens Axboe
2020-06-02  6:46             ` Ulf Hansson
2020-06-02  6:46               ` Ulf Hansson

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