From: Peter Zijlstra <peterz@infradead.org> To: Byungchul Park <byungchul.park@lge.com> 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: Mon, 24 Apr 2017 12:17:47 +0200 [thread overview] Message-ID: <20170424101747.iirvjjoq66x25w7n@hirez.programming.kicks-ass.net> (raw) In-Reply-To: <20170424051102.GJ21430@X58A-UD3R> 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. 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.
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org> To: Byungchul Park <byungchul.park@lge.com> 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: Mon, 24 Apr 2017 12:17:47 +0200 [thread overview] Message-ID: <20170424101747.iirvjjoq66x25w7n@hirez.programming.kicks-ass.net> (raw) In-Reply-To: <20170424051102.GJ21430@X58A-UD3R> 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. 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. -- 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:[~2017-04-24 10:18 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 [this message] 2017-04-24 10:17 ` Peter Zijlstra 2017-04-25 5:40 ` Byungchul Park 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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