linux-kernel - Re: [PATCH 2/2] membarrier: riscv: Provide core serializing command

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Date:   Wed, 29 Nov 2023 23:43:34 +0100
From:   Andrea Parri <parri.andrea@...il.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     paulmck@...nel.org, palmer@...belt.com, paul.walmsley@...ive.com,
        aou@...s.berkeley.edu, mmaas@...gle.com, hboehm@...gle.com,
        striker@...ibm.com, charlie@...osinc.com, rehn@...osinc.com,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] membarrier: riscv: Provide core serializing command

> > So I should probably stick to 93917ad50972, which apparently selected
> > CONFIG_MEMBARRIER on RISC-V, for the Fixes: tag in question.
> 
> I think it goes further than that, because you can explicitly
> CONFIG_MEMBARRIER=y, see init/Kconfig:
> 
> config MEMBARRIER
>         bool "Enable membarrier() system call" if EXPERT
>         default y
>         help
>           Enable the membarrier() system call that allows issuing memory
>           barriers across all running threads, which can be used to distribute
>           the cost of user-space memory barriers asymmetrically by transforming
>           pairs of memory barriers into pairs consisting of membarrier() and a
>           compiler barrier.
> 
>           If unsure, say Y.
> 
> Before 1464d00b27b2, riscv just happened to set it to =n in the defconfig.
> 
> I suspect the initial port of riscv merged after v4.14 was already broken.

I see.  Oh well, guess I'll have to leave this up to the maintainers then
(I believe I've never managed to build riscv that far), Palmer?


> > I'll look into adding the membarrier feature you mention (as a final/
> > follow-up patch), unless you or someone else want to take care of it.
> 
> I'll be happy to review it :)

Sweet!  :-)

  Andrea