linux-kernel - Re: [PATCH] powerpc/32: Don't use lmw/stmw for saving/restoring non volatile regs

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Message-Id: <163584790541.1845480.12718539739212562295.b4-ty@ellerman.id.au>
Date:   Tue, 02 Nov 2021 21:11:45 +1100
From:   Michael Ellerman <patch-notifications@...erman.id.au>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc/32: Don't use lmw/stmw for saving/restoring non volatile regs

On Mon, 23 Aug 2021 15:29:12 +0000 (UTC), Christophe Leroy wrote:
> Instructions lmw/stmw are interesting for functions that are rarely
> used and not in the cache, because only one instruction is to be
> copied into the instruction cache instead of 19. However those
> instruction are less performant than 19x raw lwz/stw as they require
> synchronisation plus one additional cycle.
> 
> SAVE_NVGPRS / REST_NVGPRS are used in only a few places which are
> mostly in interrupts entries/exits and in task switch so they are
> likely already in the cache.
> 
> [...]

Applied to powerpc/next.

[1/1] powerpc/32: Don't use lmw/stmw for saving/restoring non volatile regs
      https://git.kernel.org/powerpc/c/a85c728cb5e12216c19ae5878980c2cbbbf8616d

cheers