[Top] [All Lists]

Re: agsize and performance

To: Matthias Schniedermeyer <ms@xxxxxxx>
Subject: Re: agsize and performance
From: K T <mailkarthikt@xxxxxxxxx>
Date: Wed, 30 Oct 2013 10:46:16 -0400
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=4DM1OEnHk92yTegFweP59OHoZGu/B8vIXUHFnOq74GY=; b=Kv7uPkCBMyUXcwvK33pbysgUk72AdVUnfo0Kbyt4iebyKyQUpaOBpmKzVGLp/4S3eq 9debi0xo3inwF8OHRCVobY6TlGnsodzoKw9AvcJosnrFvbtNd4NoY1YXjEY0iMIKzRfx nCLtiIjc4Zf6FCmacWaUUpjlS1t0wicMESJB1OTN0Z7A6itT4if6558N0jinjpxxTVQW HdJNrOGMwSSu54l/vGzOsoJhtYNNWrKSKPUEZ32y0U01Q6pAAYMsop5VQ6iWEnNBn0RW Ip+l4gsGYJQpT067+2vWsUKsSZm9S7CUMD40erAHgUSmdnOXhdoRXw34i6zSLWYumL15 ukbA==
In-reply-to: <20131030095903.GA8077@xxxxxxx>
References: <CALtWs4-q==CXVZ=jjRnrZGANP98y2Gyot_DV_hGTgxQoRF25UA@xxxxxxxxxxxxxx> <20131030095903.GA8077@xxxxxxx>
I meant sync not fsync(O_SYNC flag).

My main question is why there is better throughput when I make the agsize smaller?

On Wed, Oct 30, 2013 at 5:59 AM, Matthias Schniedermeyer <ms@xxxxxxx> wrote:
On 29.10.2013 18:10, K T wrote:
> Hi,
> I have a 1 TB SATA disk(WD1003FBYX) with XFS. In my tests, I preallocate a
> bunch of 10GB files and write data to the files one at a time. I have
> observed that the default mkfs setting(4 AGs) gives very low throughput.
> When I reformat the disk with a agsize of 256mb(agcount=3726), I see better
> throughput. I thought with a bigger agsize, the files will be made of fewer
> extents and hence perform better(due to lesser entries in the extent map
> getting updated). But, according to my tests, the opposite seems to be
> true. Can you please explain why this the case? Am I missing something?
> My test parameters:
> mkfs.xfs -f /dev/sdbf1
> mount  -o inode64 /dev/sdbf1 /mnt/test
> fallocate -l 10G fname
> dd if=/dev/zero of=fname bs=2M count=64 oflag=direct,sync conv=notrunc seek=0

I get the same bad performance with your dd statement.

fallocate -l 10G fname
time dd if=/dev/zero of=fname bs=2M count=64 oflag=direct,sync conv=notrunc seek=0
64+0 records in
64+0 records out
134217728 bytes (134 MB) copied, 4,24088 s, 31,6 MB/s

After pondering the really hard to read dd-man-page.
Sync is for 'synchronized' I/O. aka REALLY BAD PERFORMANCE. And i assume
you don't really that.

I think what you meant is fsync. (a.k.a. File (and Metadata) has hit
stable-storage before dd exits).
That is: conv=fsync

time dd if=/dev/zero of=fname bs=2M count=64 oflag=direct conv=notrunc,fsync seek=0
64+0 records in
64+0 records out
134217728 bytes (134 MB) copied, 1,44088 s, 93,2 MB/s

That gets much better performance, and in my case it can't get any
better because the HDD (and encryption) just can't go any faster.



<Prev in Thread] Current Thread [Next in Thread>