From: Qu Wenruo <quwenruo.btrfs@gmx.com>
To: Supercilious Dude <supercilious.dude@gmail.com>
Cc: "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>,
Linux FS Devel <linux-fsdevel@vger.kernel.org>,
linux-block@vger.kernel.org
Subject: Re: Is it possible that certain physical disk doesn't implement flush correctly?
Date: Sat, 30 Mar 2019 21:00:26 +0800 [thread overview]
Message-ID: <16edb2d0-ee41-908f-e0bf-5c27160ccff7@gmx.com> (raw)
In-Reply-To: <CAGmvKk7bYkaNXGe4agwLWmM_YM7Sjfn1NjBheQ=FzcJmUkZcGg@mail.gmail.com>
[-- Attachment #1.1: Type: text/plain, Size: 1464 bytes --]
On 2019/3/30 下午8:57, Supercilious Dude wrote:
> Hi,
>
> This would give a false positive on any controller with a cache as all
> requests would take 0ms until the cache is full and the controller has
> to actually flush to disk.
I'm purposing to measure the execution time of flush/fsync, not write.
And if flush takes 0ms, it means it doesn't really write cached data
onto disk.
Thanks,
Qu
> I am using an HP P841 controller in my test
> system and it has a 4GB cache making every IO instant unless there are
> enough of them that they can't be flushed to the disks as quickly as
> they come in - the latency variation is huge depending on load.
>
> Regards
>
> On Sat, 30 Mar 2019 at 12:34, Qu Wenruo <quwenruo.btrfs@gmx.com> wrote:
>>
>> Hi,
>>
>> I'm wondering if it's possible that certain physical device doesn't
>> handle flush correctly.
>>
>> E.g. some vendor does some complex logical in their hdd controller to
>> skip certain flush request (but not all, obviously) to improve performance?
>>
>> Do anyone see such reports?
>>
>> And if proves to happened before, how do we users detect such problem?
>>
>> Can we just check the flush time against the write before flush call?
>> E.g. write X random blocks into that device, call fsync() on it, check
>> the execution time. Repeat Y times, and compare the avg/std.
>> And change X to 2X/4X/..., repeat above check.
>>
>> Thanks,
>> Qu
>>
>>
[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 488 bytes --]
next prev parent reply other threads:[~2019-03-30 13:00 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-30 12:31 Is it possible that certain physical disk doesn't implement flush correctly? Qu Wenruo
2019-03-30 12:57 ` Supercilious Dude
2019-03-30 13:00 ` Qu Wenruo [this message]
2019-03-30 13:04 ` Supercilious Dude
2019-03-30 13:09 ` Qu Wenruo
2019-03-30 13:14 ` Supercilious Dude
2019-03-30 13:24 ` Qu Wenruo
2019-03-31 22:45 ` J. Bruce Fields
2019-03-31 23:07 ` Alberto Bursi
2019-03-31 11:27 ` Alberto Bursi
2019-03-31 12:00 ` Qu Wenruo
2019-03-31 13:36 ` Hannes Reinecke
2019-03-31 14:17 ` Qu Wenruo
2019-03-31 14:37 ` Hannes Reinecke
2019-03-31 14:40 ` Qu Wenruo
2019-03-31 12:21 ` Andrei Borzenkov
2019-04-01 11:55 ` Austin S. Hemmelgarn
2019-04-01 12:04 ` Austin S. Hemmelgarn
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=16edb2d0-ee41-908f-e0bf-5c27160ccff7@gmx.com \
--to=quwenruo.btrfs@gmx.com \
--cc=linux-block@vger.kernel.org \
--cc=linux-btrfs@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=supercilious.dude@gmail.com \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).