All of lore.kernel.org
 help / color / mirror / Atom feed
From: Ric Wheeler <ric@emc.com>
To: Tejun Heo <htejun@gmail.com>
Cc: Jens Axboe <jens.axboe@oracle.com>,
	Robert Hancock <hancockr@shaw.ca>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-ide@vger.kernel.org, edmudama@gmail.com,
	Nicolas.Mailhot@LaPoste.net, Jeff Garzik <jeff@garzik.org>,
	Alan Cox <alan@lxorguk.ukuu.org.uk>, Mark Lord <mlord@pobox.com>,
	Dongjun Shin <d.j.shin@samsung.com>,
	Hannes Reinecke <hare@suse.de>
Subject: Re: libata FUA revisited
Date: Thu, 22 Feb 2007 17:44:59 -0500	[thread overview]
Message-ID: <45DE1CEB.4030107@emc.com> (raw)
In-Reply-To: <45DC0983.6000709@gmail.com>

Tejun Heo wrote:
> Jens Axboe wrote:
>> On Wed, Feb 21 2007, Tejun Heo wrote:
>>> [cc'ing Ric, Hannes and Dongjun, Hello.  Feel free to drag other people in.]
>>>
>>> Robert Hancock wrote:
>>>> Jens Axboe wrote:
>>>>> But we can't really change that, since you need the cache flushed before
>>>>> issuing the FUA write. I've been advocating for an ordered bit for
>>>>> years, so that we could just do:
>>>>>
>>>>> 3. w/FUA+ORDERED
>>>>>
>>>>> normal operation -> barrier issued -> write barrier FUA+ORDERED
>>>>>  -> normal operation resumes
>>>>>
>>>>> So we don't have to serialize everything both at the block and device
>>>>> level. I would have made FUA imply this already, but apparently it's not
>>>>> what MS wanted FUA for, so... The current implementations take the FUA
>>>>> bit (or WRITE FUA) as a hint to boost it to head of queue, so you are
>>>>> almost certainly going to jump ahead of already queued writes. Which we
>>>>> of course really do not.
>>> Yeah, I think if we have tagged write command and flush tagged (or
>>> barrier tagged) things can be pretty efficient.  Again, I'm much more
>>> comfortable with separate opcodes for those rather than bits changing
>>> the behavior.
>> ORDERED+FUA NCQ would still be preferable to an NCQ enabled flush
>> command, though.
> 
> I think we're talking about two different things here.
> 
> 1. The barrier write (FUA write) combined with flush.  I think it would
> help improving the performance but I think issuing two commands
> shouldn't be too slower than issuing one combined command unless it
> causes extra physical activity (moving head, etc...).
> 
> 2. FLUSH currently flushes all writes.  If we can mark certain commands
> requiring ordering, we can selectively flush or order necessary writes.
>  (No need to flush 16M buffer all over the disk when only journal needs
> barriering)

We can certainly (given time to play in the lab!) try to measure this in 
with a micro-benchmark (with an analyzer or with block trace?).

A normal flush command in my old tests seemed to be in the 20 ms range 
(mixed in with and occasional "freebie" cache flush which returns in 50 
usecs or so - cache must be empty).


>>> Another idea Dongjun talked about while drinking in LSF was ranged
>>> flush.  Not as flexible/efficient as the previous option but much less
>>> intrusive and should help quite a bit, I think.
>> But that requires extensive tracking, I'm not so sure the implementation
>> of that for barriers would be very clean. It'd probably be good for
>> fsync, though.
> 
> I was mostly thinking about journal area.  Using it for other purposes
> would incur a lot of complexity.  :-(
> 


  parent reply	other threads:[~2007-02-22 22:46 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <fa.S80SRyQbD/hm4SxliPUKU88BaCo@ifi.uio.no>
2007-02-12  5:47 ` Robert Hancock
     [not found] ` <fa.Q/csgyCHkAsD84yi+bN78H1WNNM@ifi.uio.no>
2007-02-13  0:23   ` Robert Hancock
2007-02-13 15:20     ` Tejun Heo
2007-02-14  0:07       ` Robert Hancock
2007-02-14  0:50         ` Tejun Heo
2007-02-15 18:00           ` Jens Axboe
2007-02-19 19:46             ` Robert Hancock
2007-02-21  8:37               ` Tejun Heo
2007-02-21  8:46                 ` Jens Axboe
2007-02-21  8:57                   ` Tejun Heo
2007-02-21  9:01                     ` Jens Axboe
2007-02-22 22:44                     ` Ric Wheeler [this message]
2007-02-22 22:40                   ` Ric Wheeler
2007-02-21 14:06                 ` Robert Hancock
2007-02-22 22:34                 ` Ric Wheeler
2007-02-23  0:04                   ` Robert Hancock
2007-02-21  8:44               ` Jens Axboe
2007-02-12  3:25 Robert Hancock
2007-02-12  8:31 ` Tejun Heo
2007-02-16 18:14   ` Jeff Garzik

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=45DE1CEB.4030107@emc.com \
    --to=ric@emc.com \
    --cc=Nicolas.Mailhot@LaPoste.net \
    --cc=alan@lxorguk.ukuu.org.uk \
    --cc=d.j.shin@samsung.com \
    --cc=edmudama@gmail.com \
    --cc=hancockr@shaw.ca \
    --cc=hare@suse.de \
    --cc=htejun@gmail.com \
    --cc=jeff@garzik.org \
    --cc=jens.axboe@oracle.com \
    --cc=linux-ide@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mlord@pobox.com \
    --subject='Re: libata FUA revisited' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.