From: Christoph Hellwig <hch@lst.de>
To: Palmer Dabbelt <palmer@sifive.com>
Cc: linux-riscv@lists.infradead.org, Christoph Hellwig <hch@lst.de>,
Paul Walmsley <paul.walmsley@sifive.com>
Subject: Re: [PATCH 8/8] riscv: ignore the SYS_RISCV_FLUSH_ICACHE_LOCAL flag
Date: Fri, 6 Sep 2019 19:07:25 +0200 [thread overview]
Message-ID: <20190906170725.GA13047@lst.de> (raw)
In-Reply-To: <mhng-6070e215-c109-4d92-abbc-e77a2178657d@palmer-si-x1e>
On Tue, Sep 03, 2019 at 11:46:33AM -0700, Palmer Dabbelt wrote:
> This is used by userspace as a thread-local icache barrier: there's an
> immediate fence on the current hart, and one will be executed before that
> thread makes it to userspace on another hart. As far as I can tell this is
> implemented correctly but not optimally: there's always a fence, but we
> emit an unnecessary fence when a different thread in the same context is
> scheduled on a different hart.
>
> I suppose maybe we should attach the local fence mask to a task_struct
> instead of an mm_struct, which would trade off an extra load in the
> scheduler (to check both places) or more fences in the global case (on
> every thread getting scheduled) for fewer fences in the local case. I feel
> like it's not really worth worrying about this for now.
>
> The construct seems reasonable to me.
I haven't been able to poke holes into that idea yet, but I'll try
a bit more once I find a little time.
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next prev parent reply other threads:[~2019-09-06 17:07 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-22 6:56 sys_riscv_flush_icache Christoph Hellwig
2019-08-22 6:56 ` [PATCH 1/8] riscv: fix the flags argument type for riscv_riscv_flush_icache Christoph Hellwig
2019-08-22 6:56 ` [PATCH 2/8] riscv: remove SYS_RISCV_FLUSH_ICACHE_LOCAL #define Christoph Hellwig
2019-08-22 6:56 ` [PATCH 3/8] riscv: move sys_riscv_flush_icache to cacheflush.c Christoph Hellwig
2019-08-22 6:56 ` [PATCH 4/8] riscv: remove the active_mm check in sys_riscv_flush_icache Christoph Hellwig
2019-08-22 6:56 ` [PATCH 5/8] riscv: actually clear icache_stale_mask for all harts in mm_cpumask Christoph Hellwig
2019-08-22 18:29 ` Atish Patra
2019-08-26 11:41 ` hch
2019-08-22 6:56 ` [PATCH 6/8] riscv: use get_cpu and put_cpu in sys_riscv_flush_icache Christoph Hellwig
2019-08-22 17:49 ` Atish Patra
2019-08-26 11:38 ` hch
2019-08-27 18:42 ` Atish Patra
2019-08-22 6:56 ` [PATCH 7/8] riscv: improve the local flushing logic " Christoph Hellwig
2019-08-22 17:34 ` Atish Patra
2019-08-26 11:36 ` hch
2019-08-22 6:56 ` [PATCH 8/8] riscv: ignore the SYS_RISCV_FLUSH_ICACHE_LOCAL flag Christoph Hellwig
2019-08-28 1:10 ` Palmer Dabbelt
2019-08-28 6:09 ` Christoph Hellwig
2019-09-03 18:46 ` Palmer Dabbelt
2019-09-06 17:07 ` Christoph Hellwig [this message]
2019-09-13 19:44 ` Palmer Dabbelt
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