Re: [PATCH] config: arm: omap2: remove PROVE_LOCKING from defconfig

[Lukasz Luba]

Hi Tony,

On 11/8/18 5:59 PM, Tony Lindgren wrote:
> Hi,
> 
> * Lukasz Luba <l.luba@xxxxxxxxxxxxxxxxxxx> [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.
> 
> 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.
> 
> Regards,
> 
> Tony

Regards,
Lukasz