linux-kernel - Re: [PATCH] riscv: Optimize memset

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Message-Id: <20230510035243.8586-4-zhang_fei_0403@163.com>
Date:   Wed, 10 May 2023 11:52:43 +0800
From:   zhangfei <zhang_fei_0403@....com>
To:     ajones@...tanamicro.com
Cc:     aou@...s.berkeley.edu, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, palmer@...belt.com,
        paul.walmsley@...ive.com, zhang_fei_0403@....com,
        zhangfei@...iscas.ac.cn
Subject: Re: [PATCH] riscv: Optimize memset 

From: zhangfei <zhangfei@...iscas.ac.cn>

On Tue, May 09, 2023 11:16:33AM +0200, Andrew Jones wrote: 
> On Tue, May 09, 2023 at 10:22:07AM +0800, zhangfei wrote:
> > 
> > Hi,
> > 
> > I filled head and tail with minimal branching. Each conditional ensures that 
> > all the subsequently used offsets are well-defined and in the dest region.
> 
> I know. You trimmed my comment, so I'll quote myself, here
> 
> """
> After the check of a2 against 6 above we know that offsets 6(t0)
> and -7(a3) are safe. Are we trying to avoid too may redundant
> stores with these additional checks?
> """
> 
> So, again. Why the additional check against 8 above and, the one you
> trimmed, checking 10?

Hi,

These additional checks are to avoid too many redundant stores. 

Adding a check for more than 8 bytes is because after the loop 
segment '3' comes out, the remaining bytes are less than 8 bytes, 
which also avoids redundant stores.

Thanks,
Fei Zhang