linux-kernel - Re: [PATCH v2 0/6] iomap: some minor non-critical fixes and improvements when block size

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Message-ID: <Zrwap10baOW8XeIv@dread.disaster.area>
Date: Wed, 14 Aug 2024 12:47:03 +1000
From: Dave Chinner <david@...morbit.com>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, djwong@...nel.org, hch@...radead.org,
	brauner@...nel.org, jack@...e.cz, willy@...radead.org,
	yi.zhang@...wei.com, chengzhihao1@...wei.com, yukuai3@...wei.com
Subject: Re: [PATCH v2 0/6] iomap: some minor non-critical fixes and
 improvements when block size < folio size

On Wed, Aug 14, 2024 at 10:14:01AM +0800, Zhang Yi wrote:
> On 2024/8/14 9:49, Dave Chinner wrote:
> > important to know if the changes made actually provided the benefit
> > we expected them to make....
> > 
> > i.e. this is the sort of table of results I'd like to see provided:
> > 
> > platform	base		v1		v2
> > x86		524708.0	569218.0	????
> > arm64		801965.0	871605.0	????
> > 
> 
>  platform	base		v1		v2
>  x86		524708.0	571315.0 	569218.0
>  arm64	801965.0	876077.0	871605.0

So avoiding the lock cycle in iomap_write_begin() (in patch 5) in
this partial block write workload made no difference to performance
at all, and removing a lock cycle in iomap_write_end provided all
that gain?

Is this an overwrite workload or a file extending workload? The
result implies that iomap_block_needs_zeroing() is returning false,
hence it's an overwrite workload and it's reading partial blocks
from disk. i.e. it is doing synchronous RMW cycles from the ramdisk
and so still calling the uptodate bitmap update function rather than
hitting the zeroing case and skipping it.

Hence I'm just trying to understand what the test is doing because
that tells me what the result should be...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com