linux-kernel - Re: [PATCH] xfs: optimise xfs_mod

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Date:   Mon, 4 Nov 2019 07:25:17 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Shaokun Zhang <zhangshaokun@...ilicon.com>
Cc:     linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yang Guo <guoyang2@...wei.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>
Subject: Re: [PATCH] xfs: optimise xfs_mod_icount/ifree when delta < 0

On Mon, Nov 04, 2019 at 07:29:40PM +0800, Shaokun Zhang wrote:
> From: Yang Guo <guoyang2@...wei.com>
> 
> percpu_counter_compare will be called by xfs_mod_icount/ifree to check
> whether the counter less than 0 and it is a expensive function.
> let's check it only when delta < 0, it will be good for xfs's performance.

How much overhead do you see?  In the end the compare is just a debug
check, so if it actually shows up we should remove it entirely.