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

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Message-ID: <20151103143858.GI7637@e104818-lin.cambridge.arm.com>
Date:	Tue, 3 Nov 2015 14:38:59 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Robert Richter <rric@...nel.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Robert Richter <rrichter@...ium.com>,
	Tirumalesh Chalamarla <tchalamarla@...ium.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: Increase the max granular size

On Tue, Nov 03, 2015 at 12:05:05PM +0000, Catalin Marinas wrote:
> On Tue, Nov 03, 2015 at 12:07:06PM +0100, Geert Uytterhoeven wrote:
> > On Wed, Oct 28, 2015 at 8:09 PM, Catalin Marinas
> > <catalin.marinas@....com> wrote:
> > > On Tue, Sep 22, 2015 at 07:59:48PM +0200, Robert Richter 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>
> > >
> > > Applied. Thanks.
> > 
> > This patch causes a BUG() on r8a7795/salvator-x, for which support is not
> > yet upstream.
> > 
> > My config (attached) uses SLAB. If I switch to SLUB, it works.
> > The arm64 defconfig works, even if I switch from SLUB to SLAB.
> [...]
> > ------------[ cut here ]------------
> > kernel BUG at mm/slab.c:2283!
> > Internal error: Oops - BUG: 0 [#1] SMP
> [...]
> > Call trace:
> > [<ffffffc00014f9b4>] __kmem_cache_create+0x21c/0x280
> > [<ffffffc00068be50>] create_boot_cache+0x4c/0x80
> > [<ffffffc00068bed8>] create_kmalloc_cache+0x54/0x88
> > [<ffffffc00068bfc0>] create_kmalloc_caches+0x50/0xf4
> > [<ffffffc00068db08>] kmem_cache_init+0x104/0x118
> > [<ffffffc00067d7d8>] start_kernel+0x218/0x33c
> 
> I haven't managed to reproduce this on a Juno kernel.

I now managed to reproduce it with your config (slightly adapted to
allow Juno). I'll look into it.

-- 
Catalin
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