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: Wed, 28 Aug 2019 08:09:42 +0200 [thread overview]
Message-ID: <20190828060942.GA21592@lst.de> (raw)
In-Reply-To: <mhng-363188c5-b80c-4935-8a84-861fbdb1e8e4@palmer-si-x1e>
On Tue, Aug 27, 2019 at 06:10:33PM -0700, Palmer Dabbelt wrote:
> This is meant to perform a context-local flush, not a cpu-local flush. The
> whole point here is that userspace doesn't know anything about CPUs, just
> contexts -- that's why we have this deferred flush mechanism. I think the
> logic is complicated but sound, and removing this will almost certainly
> lead to huge performance degradation.
All calls to flush_icache_mm are local to the context. Take a look at
what the current code does:
- set all bits in context.icache_stale_mask
- clear the current cpu from context.icache_stale_mask
- flush the cpu local icache
- create a local others mask containing every cpu running the context
except for the current one
- now if others is empty OR the local flag is set don't do anything
but a memory barrier, else flush the other cpus
>
> Maybe I'm missing something, what is the specific issue?
The issue is that the current implementation of
SYS_RISCV_FLUSH_ICACHE_LOCAL only flushes the icache of the currently
running core, which is an interface that can't be used correctly.
riscv_flush_icache without that flag on the other handle already just
flushes the caches for the cpus that run the current context, and then
causes a deferred flush if the context gets run on another cpu
eventually.
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next prev parent reply other threads:[~2019-08-28 6:09 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 [this message]
2019-09-03 18:46 ` Palmer Dabbelt
2019-09-06 17:07 ` Christoph Hellwig
2019-09-13 19:44 ` Palmer Dabbelt
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