From: Matthew Wilcox <willy@infradead.org>
To: Vineet Gupta <vgupta@kernel.org>
Cc: linux-snps-arc@lists.infradead.org,
Alexey Brodkin <abrodkin@synopsys.com>
Subject: Re: How many colours does the ARC cache have?
Date: Sat, 18 Feb 2023 19:03:51 +0000 [thread overview]
Message-ID: <Y/EhF1W9V+coccd6@casper.infradead.org> (raw)
In-Reply-To: <4ebe9300-c694-5a49-7180-ca6c14ec11b6@kernel.org>
On Wed, Feb 15, 2023 at 08:59:18PM -0800, Vineet Gupta wrote:
> On 2/10/23 09:06, Matthew Wilcox wrote:
> > I see a discrepancy here ...
> >
> > arch/arc/include/asm/shmparam.h:
> > /* Handle upto 2 cache bins */
> > #define SHMLBA (2 * PAGE_SIZE)
> >
> > arch/arc/include/asm/cacheflush.h:
> > #define CACHE_COLORS_NUM 4
>
> The initial aliasing dcache support assumed 2 colors but was later bumped to
> 4, w/o making the adjustment in shmparam.h
OK. Will you fix it yourself, or do you want me to send a patch?
> > (there are some other problems with the arc cache flushing code;
>
> The VIPT aliasing config (which is pretty much dead and unused) or regular
> parts ?
I'm not sure. This is incorrect in flush_dcache_page():
} else if (page_mapcount(page)) {
[...]
unsigned long vaddr = page->index << PAGE_SHIFT;
If the page being flushed is a tail page, then page->index is not
valid, so you're essentially flushing a random address. I have a
fix for it that I sent out earlier this week.
> > I'm working on patches to address them, but those are things I understand a
> > little better. I know nothing about the ARC architecture itself)
>
> Legacy ARC700 cpus had VIPT D$. The cache size was configurable by Soc
> builder and the specific geometry could yield an aliasing configuration
> (e.g. standard page size 8K, 4 way set associative D$: so D$ > 32K were
> aliasing and needed CONFIG_ARC_CACHE_VIPT_ALIASING). Although there was ever
> only 1 customer who taped out an aliasing cache config.
>
> The newer ARC HS cores have PIPT D$ and thus don't need the aliasing
> support.
>
> FWIW we could rip out all the VIPT aliasing code as I don't think it is
> needed anymore. @Alexey can you confirm ?
>
> -Vineet
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prev parent reply other threads:[~2023-02-18 19:04 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-10 17:06 How many colours does the ARC cache have? Matthew Wilcox
2023-02-16 4:59 ` Vineet Gupta
2023-02-18 19:03 ` Matthew Wilcox [this message]
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