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Date:   Mon, 4 Feb 2019 12:26:04 -0800
From:   Tony Lindgren <tony@atomide.com>
To:     Lukasz Luba <l.luba@partner.samsung.com>
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        b.zolnierkie@samsung.com, linux-omap@vger.kernel.org
Subject: Re: [PATCH] config: arm: omap2: remove PROVE_LOCKING from defconfig
Message-ID: <20190204202604.GP5720@atomide.com>
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* Lukasz Luba <l.luba@partner.samsung.com> [181113 10:22]:
> Hi Tony,
> 
> On 11/8/18 5:59 PM, Tony Lindgren wrote:
> > Hi,
> > 
> > * Lukasz Luba <l.luba@partner.samsung.com> [181009 08:36]:
> >> PROVE_LOCKING enables LOCKDEP, which causes big overhead on cache and
> >> bus transactions.
> >>
> >> On some ARM big.LITTLE architecutres (Exynos 5433) the overhead is really big.
> >> The overhead can be measures using hackbench which will speed up
> >> by x3 times (11sec -> 3.4sec).
> >> When you check transaction on cache or buses, the results are way higher
> >> than normal for the same hackbench test:
> >> L1d cache invalidations: 26mln vs 4mln
> >> L2u cache invalidations: 42mln vs 12mln
> >> bus cyc/access: 30cyc/access vs. 20cyc/access
> >> context switch is x3 times cheaper
> >>
> >> Enable this option only when you have some locking issue to investigate.
> > 
> > I'm all for this, but this disables also other less intrusive
> > debug options. It used to be that we'd get locking issues merged
> > into drivers and I think that's how it originally got enabled.
> That's common reason for a few defconfigs in mainline.

Actually looks like this does not change the DEBUG
related options.. I must have done something wrong
earlier, sorry. So applying into omap-for-v5.1/defconfig.

> > So we should take a look which ones we can or want to keep.
> > Or just disable CONFIG_DEBUG completely.
> Ideally, the CI should try a few 'types' of configs,
> generated based on the 'defconfig'. Some 'smart' script might
> cut the debug options for an image for performance regression tests.
> > 
> > For distros, that's multi_v7_defconfig nowadays for most part
> > so I think most people using omap2plus_defconfig are developers
> > working on various devices.

Yes I think that's the case.

Regards,

Tony