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Re: [PATCH] mkfs: default to CRC enabled filesystems

To: Linda Walsh <xfs@xxxxxxxxx>
Subject: Re: [PATCH] mkfs: default to CRC enabled filesystems
From: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx>
Date: Fri, 20 Mar 2015 11:38:46 -0700
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <550B858D.4030003@xxxxxxxxx>
References: <1426720967-8215-1-git-send-email-david@xxxxxxxxxxxxx> <550B858D.4030003@xxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Mar 19, 2015 at 07:27:25PM -0700, Linda Walsh wrote:
> Dave Chinner wrote:
> >From: Dave Chinner <dchinner@xxxxxxxxxx>
> >
> >It's time to change the mkfs defaults to enable CRCs for all new
> >filesystems.
> ---
>       "Sounds good", but what exactly is CRC'ed?
> 
> I.e. all data? Or how much data/second would I expect
> to 'need' CRC'ing?
> 
> Some quick timing stuff:
> 
> >time  dd if=/dev/zero of=1G bs=1M count=1024 oflag=direct
> 1024+0 records in
> 1024+0 records out
> 1073741824 bytes (1.1 GB) copied, 1.76947 s, 607 MB/s
> 1.77sec 0.00usr 0.50sys (28.38% cpu)
> 
> >dropcaches
> 76.34sec 0.00usr 69.22sys (90.69% cpu)
> 
> Ishtar:law/bin> time crc32 1G         ## no cache
> 5B64C2B0
> 6.67sec 3.85usr 0.94sys (71.82% cpu)
> 
> >time crc32 1G                                ## in cache
> 5B64C2B0
> 4.00sec 3.57usr 0.42sys (100.00% cpu)
> (using Xeon X5660 @ 2.80GHz)

Usually the kernel will load one of the CRC32c accelerators to reduce the
impact of the metadata checksumming.  Not sure if 'crc32' knows how to use
the new instructions Intel built into that X5660, though I'm guessing not.
Also, XFS uses crc32c, not crc32.

--D

> 
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