linux-kernel - Re: [PATCH] arm64: Increase the max granular size

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Message-ID: <CAOZdJXUiRMAguDV+HEJqPg57MyBNqEcTyaH+ya=U93NHb-pdJA@mail.gmail.com>
Date:	Fri, 16 Oct 2015 14:57:30 -0500
From:	Timur Tabi <timur@...eaurora.org>
To:	Robert Richter <rric@...nel.org>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Robert Richter <rrichter@...ium.com>,
	Tirumalesh Chalamarla <tchalamarla@...ium.com>,
	lkml <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: Increase the max granular size

On Tue, Sep 22, 2015 at 12:59 PM, Robert Richter <rric@...nel.org> wrote:
> From: Tirumalesh Chalamarla <tchalamarla@...ium.com>
>
> Increase the standard cacheline size to avoid having locks in the same
> cacheline.
>
> Cavium's ThunderX core implements cache lines of 128 byte size. With
> current granulare size of 64 bytes (L1_CACHE_SHIFT=6) two locks could
> share the same cache line leading a performance degradation.
> Increasing the size fixes that.
>
> Increasing the size has no negative impact to cache invalidation on
> systems with a smaller cache line. There is an impact on memory usage,
> but that's not too important for arm64 use cases.
>
> Signed-off-by: Tirumalesh Chalamarla <tchalamarla@...ium.com>
> Signed-off-by: Robert Richter <rrichter@...ium.com>

Acked-by: Timur Tabi <timur@...eaurora.org>

We need this patch, because on our silicon, CTR_EL0[CWG] set to 5, which
means that setup_processor() complains with this warning:

cls = cache_line_size();

if (L1_CACHE_BYTES < cls)
    pr_warn("L1_CACHE_BYTES smaller than the Cache Writeback Granule
(%d < %d)\n",
            L1_CACHE_BYTES, cls);

-- 
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.
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