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Wed, 10 Oct 2018 08:42:57 +0000 (GMT) Subject: Re: [PATCH] lib/Kconfig.debug: add a comment to PROVE_LOCKING impact To: Waiman Long , linux-kernel@vger.kernel.org Cc: b.zolnierkie@samsung.com, mingo@redhat.com From: Lukasz Luba Date: Wed, 10 Oct 2018 10:42:55 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US Content-Transfer-Encoding: 7bit X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFupnleLIzCtJLcpLzFFi42LZduznOd1Ju/dGG6zcomCxccZ6VovLu+aw WZw+doLF4tKBBUwOLB7v911l8+jbsorR4/MmuQDmKC6blNSczLLUIn27BK6Mxve/mAtOi1Ys bGtia2DsEuxi5OSQEDCRWH3iLHsXIxeHkMAKRonHh38xQjhfGCXaL/9nhnA+M0osez6bDaZl 4c09UFXLGSWmvdjJAuG8ZZR4t3w/O0iVsIC/xOzjP1lBbBEBJ4lX0yYAFXFwMAvoSfy5oQJi sgGZO1YVglSwCKhKLFjxEqxTVCBC4siDhYwgNq+AoMTJmU9YQGxOATuJbWefgtnMAuISt57M Z4Kw5SW2v50DdqiEQDe7xJEZLawQzWUSfY33WCGOdpE48PctE4QtLPHq+BZ2CFtG4v/O+VDx YomzHaugnqyRaD+5A6rGWuLw8YusEOdrSqzfpQ8RdpTY8OcVI0hYQoBP4sZbQYhz+CQmbZvO DBHmlehoE4Ko1pDY0nMBapGYxPI109gnMCrNQvLkLCSPzULy2CyEvQsYWVYxiqeWFuempxYb 5aWW6xUn5haX5qXrJefnbmIEJpPT/45/2cG460/SIUYBDkYlHt6GC3uihVgTy4orcw8xSnAw K4nw7n4IFOJNSaysSi3Kjy8qzUktPsQozcGiJM67bN7GaCGB9MSS1OzU1ILUIpgsEwenVAPj pKCij/yqQkoFZ+ZM2HInJ2OR5v8rJU65r/LyOb7JGU05sqGWZftjvT1n5T6u6n2QlFy0tTmx 0ajrO//vWFHNq4fLSped2nzv8ErOCLbt9ybv3b3KkcGnba9HV/AJk7bFV5XPHP1sJSe90XIt /1KfY/eVZ5fOlZJ4lRJ+xsDl2sTY4i8FsoVPlViKMxINtZiLihMB58XeEiIDAAA= X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFlrEIsWRmVeSWpSXmKPExsVy+t/xe7oTd++NNljbpWyxccZ6VovLu+aw WZw+doLF4tKBBUwOLB7v911l8+jbsorR4/MmuQDmKD2bovzSklSFjPziElulaEMLIz1DSws9 IxNLPUNj81grI1MlfTublNSczLLUIn27BL2Mxve/mAtOi1YsbGtia2DsEuxi5OSQEDCRWHhz D2MXIxeHkMBSRonJvUdZIBJiEpP2bWeHsIUl/lzrYgOxhQReM0p0zJIDsYUFfCUmbWhhBbFF BJwkXk2bANTLwcEsoCfx54YKxMx/jBKzF75kA4mzAcV3rCoEKecVcJM4fGA62EgWAVWJBSte gq0SFYiQWL38BStEjaDEyZlPwM7hFLCT2Hb2KZjNLGAmMW/zQ2YIW1zi1pP5TBC2vMT2t3OY JzAKzULSPgtJyywkLbOQtCxgZFnFKJJaWpybnltsqFecmFtcmpeul5yfu4kRGD/bjv3cvIPx 0sbgQ4wCHIxKPLwNF/ZEC7EmlhVX5h5ilOBgVhLh3f0QKMSbklhZlVqUH19UmpNafIjRFOi5 icxSosn5wNjOK4k3NDU0t7A0NDc2NzazUBLnPW9QGSUkkJ5YkpqdmlqQWgTTx8TBKdXAKKoT pvDg3+JDnybcUeY1fnLh/rtFn5YbPJJ5knk4zyL6pHn/Xp/4fX4MbmGLNvIrRJgqzRdqunf+ 3kdFOUPDhVVCWl8NVgo8mm+SKyjOqbJRlqf+45H9p+oYz/nedKm6d2KVmLAla/ND4dVXlH/0 2bE4HAr8tm7l0z4vhtaZTby6s/5O4p+xX4mlOCPRUIu5qDgRAIKiTmi1AgAA Message-Id: <20181010084257eucas1p14a7e3c9e7931e7151f9ea5e8ae415dc0~cMsEsFmFC0910909109eucas1p1h@eucas1p1.samsung.com> X-CMS-MailID: 20181010084257eucas1p14a7e3c9e7931e7151f9ea5e8ae415dc0 X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" X-RootMTR: 20181009153959eucas1p1ab3c10ba4868a4e97a1bff24d8f34c41 X-EPHeader: CA CMS-TYPE: 201P X-CMS-RootMailID: 20181009153959eucas1p1ab3c10ba4868a4e97a1bff24d8f34c41 References: <20181009153959eucas1p1ab3c10ba4868a4e97a1bff24d8f34c41~b_u5xrZ3z3130331303eucas1p1U@eucas1p1.samsung.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Longman, Thanks for the patches. I have applied them and run on ARM. In context switch test, there is ~2% improvement (but still ~15us instead of 5-6us). In dhrystone: test results are the same. There is also 2% improvement in boot time. You can add me on CC list if you have some patches related to this feature. I will give it a try on arm platforms. Regards, Lukasz On 10/09/2018 07:29 PM, Waiman Long wrote: > On 10/09/2018 11:39 AM, Lukasz Luba wrote: >> This patch add some comment related to performance impact, >> which can be really big (x3 times slower context switch). >> >> Signed-off-by: Lukasz Luba >> --- >> lib/Kconfig.debug | 11 +++++++++++ >> 1 file changed, 11 insertions(+) >> >> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug >> index 4966c4f..9e67a2a3 100644 >> --- a/lib/Kconfig.debug >> +++ b/lib/Kconfig.debug >> @@ -1088,6 +1088,9 @@ config PROVE_LOCKING >> the proof of observed correctness is also maintained for an >> arbitrary combination of these separate locking variants. >> >> + This feature enables LOCKDEP which can harm system performance >> + even x3 times. >> + >> For more details, see Documentation/locking/lockdep-design.txt. >> >> config LOCK_STAT >> @@ -1112,6 +1115,10 @@ config LOCK_STAT >> CONFIG_LOCK_STAT defines "contended" and "acquired" lock events. >> (CONFIG_LOCKDEP defines "acquire" and "release" events.) >> >> + This feature enables LOCKDEP which can harm system performance >> + even x3 times. >> + For more details, see Documentation/locking/lockdep-design.txt. >> + >> config DEBUG_RT_MUTEXES >> bool "RT Mutex debugging, deadlock detection" >> depends on DEBUG_KERNEL && RT_MUTEXES >> @@ -1175,6 +1182,10 @@ config DEBUG_LOCK_ALLOC >> spin_lock_init()/mutex_init()/etc., or whether there is any lock >> held during task exit. >> >> + This feature enables LOCKDEP which can harm system performance >> + even x3 times. >> + For more details, see Documentation/locking/lockdep-design.txt. >> + >> config LOCKDEP >> bool >> depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT > > I don't mind seeing warning message about the performance impact of > enabling lockdep. However, the actual slowdown depends on many factors > including the type of systems, workloads and so on. I am a bit hesitant > to quote an actual figure like x3 in the help text as it may not be > correct in many cases. > > BTW, my recent lockdep patch (https://lkml.org/lkml/2018/10/2/1410) > should be able to reduce the performance impact of enabling lockdep. > Could you try to see if that help in your case? > > Cheers, > Longman > > > >