From: Byungchul Park <byungchul.park@lge.com> To: Peter Zijlstra <peterz@infradead.org> Cc: <mingo@kernel.org>, <tglx@linutronix.de>, <walken@google.com>, <boqun.feng@gmail.com>, <kirill@shutemov.name>, <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>, <iamjoonsoo.kim@lge.com>, <akpm@linux-foundation.org>, <willy@infradead.org>, <npiggin@gmail.com>, <kernel-team@lge.com> Subject: Re: [PATCH v6 05/15] lockdep: Implement crossrelease feature Date: Tue, 25 Apr 2017 14:40:44 +0900 [thread overview] Message-ID: <20170425054044.GK21430@X58A-UD3R> (raw) In-Reply-To: <20170424101747.iirvjjoq66x25w7n@hirez.programming.kicks-ass.net> On Mon, Apr 24, 2017 at 12:17:47PM +0200, Peter Zijlstra wrote: > On Mon, Apr 24, 2017 at 02:11:02PM +0900, Byungchul Park wrote: > > On Wed, Apr 19, 2017 at 04:25:03PM +0200, Peter Zijlstra wrote: > > > > I still don't like work_id; it doesn't have anything to do with > > > workqueues per se, other than the fact that they end up using it. > > > > > > It's a history generation id; touching it completely invalidates our > > > history. Workqueues need this because they run independent work from the > > > same context. > > > > > > But the same is true for other sites. Last time I suggested > > > lockdep_assert_empty() to denote all suck places (and note we already > > > have lockdep_sys_exit() that hooks into the return to user path). > > > > I'm sorry but I don't understand what you intend. It would be appriciated > > if you explain more. > > > > You might know why I introduced the 'work_id'.. Is there any alternative? > > My complaint is mostly about naming.. and "hist_gen_id" might be a > better name. Ah, I also think the name, 'work_id', is not good... and frankly I am not sure if 'hist_gen_id' is good, either. What about to apply 'rollback', which I did for locks in irq, into works of workqueues? If you say yes, I will try to do it. > But let me explain. > > > The reason workqueues need this is because the lock history for each > 'work' are independent. The locks of Work-B do not depend on the locks > of the preceding Work-A, because the completion of Work-B is not > dependent on those locks. > > But this is true for many things; pretty much all kthreads fall in this > pattern, where they have an 'idle' state and future completions do not > depend on past completions. Its just that since they all have the 'same' > form -- the kthread does the same over and over -- it doesn't matter > much. > > The same is true for system-calls, once a system call is complete (we've > returned to userspace) the next system call does not depend on the lock > history of the previous one. Yes. I agree. As you said, actually two independent job e.g. syscalls, works.. should not depend on each other. Frankly speaking, nevertheless, if they depend on each other, then I think it would be better to detect the cases, too. But for now, since it's more important to avoid false positive detections, I will do it as conservatively as possible, as my current implementation. And thank you for additional explanation!
WARNING: multiple messages have this Message-ID (diff)
From: Byungchul Park <byungchul.park@lge.com> To: Peter Zijlstra <peterz@infradead.org> Cc: mingo@kernel.org, tglx@linutronix.de, walken@google.com, boqun.feng@gmail.com, kirill@shutemov.name, linux-kernel@vger.kernel.org, linux-mm@kvack.org, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, willy@infradead.org, npiggin@gmail.com, kernel-team@lge.com Subject: Re: [PATCH v6 05/15] lockdep: Implement crossrelease feature Date: Tue, 25 Apr 2017 14:40:44 +0900 [thread overview] Message-ID: <20170425054044.GK21430@X58A-UD3R> (raw) In-Reply-To: <20170424101747.iirvjjoq66x25w7n@hirez.programming.kicks-ass.net> On Mon, Apr 24, 2017 at 12:17:47PM +0200, Peter Zijlstra wrote: > On Mon, Apr 24, 2017 at 02:11:02PM +0900, Byungchul Park wrote: > > On Wed, Apr 19, 2017 at 04:25:03PM +0200, Peter Zijlstra wrote: > > > > I still don't like work_id; it doesn't have anything to do with > > > workqueues per se, other than the fact that they end up using it. > > > > > > It's a history generation id; touching it completely invalidates our > > > history. Workqueues need this because they run independent work from the > > > same context. > > > > > > But the same is true for other sites. Last time I suggested > > > lockdep_assert_empty() to denote all suck places (and note we already > > > have lockdep_sys_exit() that hooks into the return to user path). > > > > I'm sorry but I don't understand what you intend. It would be appriciated > > if you explain more. > > > > You might know why I introduced the 'work_id'.. Is there any alternative? > > My complaint is mostly about naming.. and "hist_gen_id" might be a > better name. Ah, I also think the name, 'work_id', is not good... and frankly I am not sure if 'hist_gen_id' is good, either. What about to apply 'rollback', which I did for locks in irq, into works of workqueues? If you say yes, I will try to do it. > But let me explain. > > > The reason workqueues need this is because the lock history for each > 'work' are independent. The locks of Work-B do not depend on the locks > of the preceding Work-A, because the completion of Work-B is not > dependent on those locks. > > But this is true for many things; pretty much all kthreads fall in this > pattern, where they have an 'idle' state and future completions do not > depend on past completions. Its just that since they all have the 'same' > form -- the kthread does the same over and over -- it doesn't matter > much. > > The same is true for system-calls, once a system call is complete (we've > returned to userspace) the next system call does not depend on the lock > history of the previous one. Yes. I agree. As you said, actually two independent job e.g. syscalls, works.. should not depend on each other. Frankly speaking, nevertheless, if they depend on each other, then I think it would be better to detect the cases, too. But for now, since it's more important to avoid false positive detections, I will do it as conservatively as possible, as my current implementation. And thank you for additional explanation! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-04-25 5:42 UTC|newest] Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-03-14 8:18 [PATCH v6 00/15] lockdep: Implement crossrelease feature Byungchul Park 2017-03-14 8:18 ` Byungchul Park 2017-03-14 8:18 ` [PATCH v6 01/15] lockdep: Refactor lookup_chain_cache() Byungchul Park 2017-03-14 8:18 ` Byungchul Park 2017-03-14 8:18 ` [PATCH v6 02/15] lockdep: Add a function building a chain between two classes Byungchul Park 2017-03-14 8:18 ` Byungchul Park 2017-03-14 8:18 ` [PATCH v6 03/15] lockdep: Change the meaning of check_prev_add()'s return value Byungchul Park 2017-03-14 8:18 ` Byungchul Park 2017-03-14 8:18 ` [PATCH v6 04/15] lockdep: Make check_prev_add() able to handle external stack_trace Byungchul Park 2017-03-14 8:18 ` Byungchul Park 2017-03-14 8:18 ` [PATCH v6 05/15] lockdep: Implement crossrelease feature Byungchul Park 2017-03-14 8:18 ` Byungchul Park 2017-04-19 14:25 ` Peter Zijlstra 2017-04-19 14:25 ` Peter Zijlstra 2017-04-24 5:11 ` Byungchul Park 2017-04-24 5:11 ` Byungchul Park 2017-04-24 10:17 ` Peter Zijlstra 2017-04-24 10:17 ` Peter Zijlstra 2017-04-25 5:40 ` Byungchul Park [this message] 2017-04-25 5:40 ` Byungchul Park 2017-05-16 14:18 ` Peter Zijlstra 2017-05-16 14:18 ` Peter Zijlstra 2017-05-18 6:22 ` Byungchul Park 2017-05-18 6:22 ` Byungchul Park 2017-04-19 15:08 ` Peter Zijlstra 2017-04-19 15:08 ` Peter Zijlstra 2017-04-24 4:36 ` Byungchul Park 2017-04-24 4:36 ` Byungchul Park 2017-04-19 17:19 ` Peter Zijlstra 2017-04-19 17:19 ` Peter Zijlstra 2017-04-24 3:04 ` Byungchul Park 2017-04-24 3:04 ` Byungchul Park 2017-04-24 9:30 ` Peter Zijlstra 2017-04-24 9:30 ` Peter Zijlstra 2017-04-25 6:59 ` Byungchul Park 2017-04-25 6:59 ` Byungchul Park 2017-04-19 17:20 ` Peter Zijlstra 2017-04-19 17:20 ` Peter Zijlstra 2017-04-24 3:13 ` Byungchul Park 2017-04-24 3:13 ` Byungchul Park 2017-05-19 8:07 ` Byungchul Park 2017-05-19 8:07 ` Byungchul Park 2017-05-19 10:30 ` Peter Zijlstra 2017-05-19 10:30 ` Peter Zijlstra 2017-05-19 10:56 ` Byungchul Park 2017-05-19 10:56 ` Byungchul Park 2017-03-14 8:18 ` [PATCH v6 06/15] lockdep: Handle non(or multi)-acquisition of a crosslock Byungchul Park 2017-03-14 8:18 ` Byungchul Park 2017-03-14 8:18 ` [PATCH v6 07/15] lockdep: Avoid adding redundant direct links of crosslocks Byungchul Park 2017-03-14 8:18 ` Byungchul Park 2017-03-14 8:18 ` [PATCH v6 08/15] lockdep: Fix incorrect condition to print bug msgs for MAX_LOCKDEP_CHAIN_HLOCKS Byungchul Park 2017-03-14 8:18 ` Byungchul Park 2017-03-14 8:18 ` [PATCH v6 09/15] lockdep: Make print_circular_bug() aware of crossrelease Byungchul Park 2017-03-14 8:18 ` Byungchul Park 2017-03-14 8:18 ` [PATCH v6 10/15] lockdep: Apply crossrelease to completions Byungchul Park 2017-03-14 8:18 ` Byungchul Park 2017-03-14 8:18 ` [PATCH v6 11/15] pagemap.h: Remove trailing white space Byungchul Park 2017-03-14 8:18 ` Byungchul Park 2017-03-14 8:18 ` [PATCH v6 12/15] lockdep: Apply crossrelease to PG_locked locks Byungchul Park 2017-03-14 8:18 ` Byungchul Park 2017-03-14 8:19 ` [PATCH v6 13/15] lockdep: Apply lock_acquire(release) on __Set(__Clear)PageLocked Byungchul Park 2017-03-14 8:19 ` Byungchul Park 2017-03-14 8:19 ` [PATCH v6 14/15] lockdep: Move data of CONFIG_LOCKDEP_PAGELOCK from page to page_ext Byungchul Park 2017-03-14 8:19 ` Byungchul Park 2017-03-14 8:19 ` [PATCH v6 15/15] lockdep: Crossrelease feature documentation Byungchul Park 2017-03-14 8:19 ` Byungchul Park
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