From: Peter Zijlstra <peterz@infradead.org> To: Andrew Murray <andrew.murray@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com>, Boqun Feng <boqun.feng@gmail.com>, Will Deacon <will.deacon@arm.com>, linux-arm-kernel@lists.infradead.org, Ard.Biesheuvel@arm.com Subject: Re: [PATCH v1 0/5] arm64: avoid out-of-line ll/sc atomics Date: Fri, 17 May 2019 14:05:22 +0200 Message-ID: <20190517120522.GM2623@hirez.programming.kicks-ass.net> (raw) In-Reply-To: <20190517100802.GS8268@e119886-lin.cambridge.arm.com> On Fri, May 17, 2019 at 11:08:03AM +0100, Andrew Murray wrote: > I think the alternative solution (excuse the pun) that you are suggesting > is to put the body of the ll/sc or LSE code in the ALTERNATIVE oldinstr/newinstr > blocks (i.e. drop the fallback branches). However this still gives us some > bloat (but less than my current solution) because we're still now inlining the > larger fallback ll/sc whereas previously they were non-inline'd functions. We > still end up with potentially unnecessary clobbers for LSE code with this > Approach prior to this series: > Approach using alternative without braces: > > LSE > LSE > NOP > NOP > > or > > LL/SC <- inlined LL/SC and thus duplicated > LL/SC > LL/SC > LL/SC Yes that. And if you worry about the extra clobber for LL/SC, you could always stuck a few PUSH/POPs around the LL/SC block. Although I'm not exactly sure where the x16,x17,x30 clobbers come from; then I look at the LL/SC code, there aren't any hard-coded regs in there. Also, the safe approach is to emit LL/SC as the default and only patch in LSE when you know the machine supports them. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply index Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-05-16 15:53 Andrew Murray 2019-05-16 15:53 ` [PATCH v1 1/5] jump_label: Don't warn on __exit jump entries Andrew Murray 2019-05-16 15:53 ` [PATCH v1 2/5] arm64: Use correct ll/sc atomic constraints Andrew Murray 2019-05-16 15:53 ` [PATCH v1 3/5] arm64: atomics: avoid out-of-line ll/sc atomics Andrew Murray 2019-05-16 15:53 ` [PATCH v1 4/5] arm64: avoid using hard-coded registers for LSE atomics Andrew Murray 2019-05-16 15:53 ` [PATCH v1 5/5] arm64: atomics: remove atomic_ll_sc compilation unit Andrew Murray 2019-05-17 7:24 ` [PATCH v1 0/5] arm64: avoid out-of-line ll/sc atomics Peter Zijlstra 2019-05-17 10:08 ` Andrew Murray 2019-05-17 10:29 ` Ard Biesheuvel 2019-05-22 10:45 ` Andrew Murray 2019-05-22 11:44 ` Ard Biesheuvel 2019-05-22 15:36 ` Andrew Murray 2019-05-17 12:05 ` Peter Zijlstra [this message] 2019-05-17 12:19 ` Ard Biesheuvel
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