Hi Krzysztof, Is it still valid that the Exynos has locking issues? Or is it enabled 'just-in-case'? On arm64 the config misses that setting. Should be enabled there as well? You have introduced this entry a year ago, probably during bug investigation.
The issue is in lockdep, the setting which enables it in Exynos is prove_locking. For now, just get rid of the second. My tests showed lockdep impact and not other minor debug features enabled. Regards, Lukasz On 10/10/2018 11:18 AM, Krzysztof Kozlowski wrote: > On Tue, 9 Oct 2018 at 17:34, Lukasz Luba <[email protected]> wrote: >> >> 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 test 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. >> >> Signed-off-by: Lukasz Luba <[email protected]> >> --- >> arch/arm/configs/exynos_defconfig | 1 - >> 1 file changed, 1 deletion(-) >> >> diff --git a/arch/arm/configs/exynos_defconfig >> b/arch/arm/configs/exynos_defconfig >> index 27ea6dfc..fbf52f3 100644 >> --- a/arch/arm/configs/exynos_defconfig >> +++ b/arch/arm/configs/exynos_defconfig >> @@ -324,7 +324,6 @@ CONFIG_MAGIC_SYSRQ=y >> CONFIG_DEBUG_KERNEL=y >> CONFIG_SOFTLOCKUP_DETECTOR=y >> # CONFIG_DETECT_HUNG_TASK is not set >> -CONFIG_PROVE_LOCKING=y > > You just disabled all debugging around locks (so also basic checks). > You did not describe this in the message... and it also makes me > wonder what were you testing? Kernel without any lock debugging (so > this patch) or kernel without lockdep only (not this patch). > > As for the reason behind this change, I am not sure. We had locking > issues and this change really helped us to spot them. Most of the > issues are solved so maybe this is not needed anymore but on the other > hand - this is development/debugging config, not a distro-ready. It > might serve as a reference for distro configs but clearly it is not > for production. > > Best regards, > Krzysztof > >> CONFIG_DEBUG_ATOMIC_SLEEP=y >> CONFIG_DEBUG_USER=y >> CONFIG_CRYPTO_RSA=m >> -- >> 2.7.4 >> > >
