From: Andrew Morton <akpm@linux-foundation.org> To: Tejun Heo <tj@kernel.org> Cc: Chris Metcalf <cmetcalf@tilera.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Thomas Gleixner <tglx@linutronix.de>, Frederic Weisbecker <fweisbec@gmail.com>, Cody P Schafer <cody@linux.vnet.ibm.com> Subject: Re: [PATCH v4 2/2] mm: make lru_add_drain_all() selective Date: Tue, 13 Aug 2013 13:31:35 -0700 [thread overview] Message-ID: <20130813133135.3b580af557d1457e4ee8331a@linux-foundation.org> (raw) In-Reply-To: <20130813201958.GA28996@mtj.dyndns.org> On Tue, 13 Aug 2013 16:19:58 -0400 Tejun Heo <tj@kernel.org> wrote: > Hello, > > On Tue, Aug 13, 2013 at 12:35:12PM -0700, Andrew Morton wrote: > > I don't know how lots-of-kmallocs compares with alloc_percpu() > > performance-wise. > > If this is actually performance sensitive, I've always assumed that it isn't performance-sensitive. schedule_on_each_cpu() has to be slow as a dog. Then again, why does this patchset exist? It's a performance optimisation so presumably someone cares. But not enough to perform actual measurements :( > the logical thing to do > would be pre-allocating per-cpu buffers instead of depending on > dynamic allocation. Do the invocations need to be stackable? schedule_on_each_cpu() calls should if course happen concurrently, and there's the question of whether we wish to permit async schedule_on_each_cpu(). Leaving the calling CPU twiddling thumbs until everyone has finished is pretty sad if the caller doesn't want that. > > That being said, the `cpumask_var_t mask' which was added to > > lru_add_drain_all() is unneeded - it's just a temporary storage which > > can be eliminated by creating a schedule_on_each_cpu_cond() or whatever > > which is passed a function pointer of type `bool (*call_needed)(int > > cpu, void *data)'. > > I'd really like to avoid that. Decision callbacks tend to get abused > quite often and it's rather sad to do that because cpumask cannot be > prepared and passed around. Can't it just preallocate all necessary > resources? I don't recall seeing such abuse. It's a very common and powerful tool, and not implementing it because some dummy may abuse it weakens the API for all non-dummies. That allocation is simply unneeded.
WARNING: multiple messages have this Message-ID (diff)
From: Andrew Morton <akpm@linux-foundation.org> To: Tejun Heo <tj@kernel.org> Cc: Chris Metcalf <cmetcalf@tilera.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Thomas Gleixner <tglx@linutronix.de>, Frederic Weisbecker <fweisbec@gmail.com>, Cody P Schafer <cody@linux.vnet.ibm.com> Subject: Re: [PATCH v4 2/2] mm: make lru_add_drain_all() selective Date: Tue, 13 Aug 2013 13:31:35 -0700 [thread overview] Message-ID: <20130813133135.3b580af557d1457e4ee8331a@linux-foundation.org> (raw) In-Reply-To: <20130813201958.GA28996@mtj.dyndns.org> On Tue, 13 Aug 2013 16:19:58 -0400 Tejun Heo <tj@kernel.org> wrote: > Hello, > > On Tue, Aug 13, 2013 at 12:35:12PM -0700, Andrew Morton wrote: > > I don't know how lots-of-kmallocs compares with alloc_percpu() > > performance-wise. > > If this is actually performance sensitive, I've always assumed that it isn't performance-sensitive. schedule_on_each_cpu() has to be slow as a dog. Then again, why does this patchset exist? It's a performance optimisation so presumably someone cares. But not enough to perform actual measurements :( > the logical thing to do > would be pre-allocating per-cpu buffers instead of depending on > dynamic allocation. Do the invocations need to be stackable? schedule_on_each_cpu() calls should if course happen concurrently, and there's the question of whether we wish to permit async schedule_on_each_cpu(). Leaving the calling CPU twiddling thumbs until everyone has finished is pretty sad if the caller doesn't want that. > > That being said, the `cpumask_var_t mask' which was added to > > lru_add_drain_all() is unneeded - it's just a temporary storage which > > can be eliminated by creating a schedule_on_each_cpu_cond() or whatever > > which is passed a function pointer of type `bool (*call_needed)(int > > cpu, void *data)'. > > I'd really like to avoid that. Decision callbacks tend to get abused > quite often and it's rather sad to do that because cpumask cannot be > prepared and passed around. Can't it just preallocate all necessary > resources? I don't recall seeing such abuse. It's a very common and powerful tool, and not implementing it because some dummy may abuse it weakens the API for all non-dummies. That allocation is simply unneeded. -- 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:[~2013-08-13 20:31 UTC|newest] Thread overview: 104+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-08-06 20:22 [PATCH] mm: make lru_add_drain_all() selective Chris Metcalf 2013-08-06 20:22 ` Chris Metcalf 2013-08-06 20:22 ` [PATCH v2] " Chris Metcalf 2013-08-06 20:22 ` Chris Metcalf 2013-08-07 20:45 ` Tejun Heo 2013-08-07 20:45 ` Tejun Heo 2013-08-07 20:49 ` [PATCH v3 1/2] workqueue: add new schedule_on_cpu_mask() API Chris Metcalf 2013-08-07 20:49 ` Chris Metcalf 2013-08-07 20:52 ` [PATCH v3 2/2] mm: make lru_add_drain_all() selective Chris Metcalf 2013-08-07 20:52 ` Chris Metcalf 2013-08-07 22:48 ` [PATCH v2] " Cody P Schafer 2013-08-07 22:48 ` Cody P Schafer 2013-08-07 20:49 ` [PATCH v4 1/2] workqueue: add new schedule_on_cpu_mask() API Chris Metcalf 2013-08-07 20:49 ` Chris Metcalf 2013-08-09 15:02 ` Tejun Heo 2013-08-09 15:02 ` Tejun Heo 2013-08-09 16:12 ` Chris Metcalf 2013-08-09 16:12 ` Chris Metcalf 2013-08-09 16:30 ` Tejun Heo 2013-08-09 16:30 ` Tejun Heo 2013-08-07 20:49 ` [PATCH v5 " Chris Metcalf 2013-08-07 20:49 ` Chris Metcalf 2013-08-09 17:40 ` Tejun Heo 2013-08-09 17:40 ` Tejun Heo 2013-08-09 17:49 ` [PATCH v6 " Chris Metcalf 2013-08-09 17:49 ` Chris Metcalf 2013-08-09 17:52 ` [PATCH v6 2/2] mm: make lru_add_drain_all() selective Chris Metcalf 2013-08-09 17:52 ` Chris Metcalf 2013-08-07 20:52 ` [PATCH v5 " Chris Metcalf 2013-08-07 20:52 ` Chris Metcalf 2013-08-07 20:52 ` [PATCH v4 " Chris Metcalf 2013-08-07 20:52 ` Chris Metcalf 2013-08-12 21:05 ` Andrew Morton 2013-08-12 21:05 ` Andrew Morton 2013-08-13 1:53 ` Chris Metcalf 2013-08-13 1:53 ` Chris Metcalf 2013-08-13 19:35 ` Andrew Morton 2013-08-13 19:35 ` Andrew Morton 2013-08-13 20:19 ` Tejun Heo 2013-08-13 20:19 ` Tejun Heo 2013-08-13 20:31 ` Andrew Morton [this message] 2013-08-13 20:31 ` Andrew Morton 2013-08-13 20:59 ` Chris Metcalf 2013-08-13 20:59 ` Chris Metcalf 2013-08-13 21:13 ` Andrew Morton 2013-08-13 21:13 ` Andrew Morton 2013-08-13 22:13 ` Chris Metcalf 2013-08-13 22:13 ` Chris Metcalf 2013-08-13 22:26 ` Andrew Morton 2013-08-13 22:26 ` Andrew Morton 2013-08-13 23:04 ` Chris Metcalf 2013-08-13 23:04 ` Chris Metcalf 2013-08-13 22:51 ` [PATCH v7 1/2] workqueue: add schedule_on_each_cpu_cond Chris Metcalf 2013-08-13 22:51 ` Chris Metcalf 2013-08-13 22:53 ` [PATCH v7 2/2] mm: make lru_add_drain_all() selective Chris Metcalf 2013-08-13 22:53 ` Chris Metcalf 2013-08-13 23:29 ` Tejun Heo 2013-08-13 23:29 ` Tejun Heo 2013-08-13 23:32 ` Chris Metcalf 2013-08-13 23:32 ` Chris Metcalf 2013-08-14 6:46 ` Andrew Morton 2013-08-14 6:46 ` Andrew Morton 2013-08-14 13:05 ` Tejun Heo 2013-08-14 13:05 ` Tejun Heo 2013-08-14 16:03 ` Chris Metcalf 2013-08-14 16:03 ` Chris Metcalf 2013-08-14 16:57 ` Tejun Heo 2013-08-14 16:57 ` Tejun Heo 2013-08-14 17:18 ` Chris Metcalf 2013-08-14 17:18 ` Chris Metcalf 2013-08-14 20:07 ` Tejun Heo 2013-08-14 20:07 ` Tejun Heo 2013-08-14 20:22 ` [PATCH v8] " Chris Metcalf 2013-08-14 20:22 ` Chris Metcalf 2013-08-14 20:44 ` Andrew Morton 2013-08-14 20:44 ` Andrew Morton 2013-08-14 20:50 ` Tejun Heo 2013-08-14 20:50 ` Tejun Heo 2013-08-14 21:03 ` Andrew Morton 2013-08-14 21:03 ` Andrew Morton 2013-08-14 21:07 ` Andrew Morton 2013-08-14 21:07 ` Andrew Morton 2013-08-14 21:12 ` Andrew Morton 2013-08-14 21:12 ` Andrew Morton 2013-08-14 21:23 ` Chris Metcalf 2013-08-14 21:23 ` Chris Metcalf 2013-08-13 23:44 ` [PATCH v7 2/2] " Chris Metcalf 2013-08-13 23:44 ` Chris Metcalf 2013-08-13 23:51 ` Tejun Heo 2013-08-13 23:51 ` Tejun Heo 2013-08-13 21:07 ` [PATCH v4 " Tejun Heo 2013-08-13 21:07 ` Tejun Heo 2013-08-13 21:16 ` Andrew Morton 2013-08-13 21:16 ` Andrew Morton 2013-08-13 22:07 ` Tejun Heo 2013-08-13 22:07 ` Tejun Heo 2013-08-13 22:18 ` Andrew Morton 2013-08-13 22:18 ` Andrew Morton 2013-08-13 22:33 ` Tejun Heo 2013-08-13 22:33 ` Tejun Heo 2013-08-13 22:47 ` Andrew Morton 2013-08-13 22:47 ` Andrew Morton 2013-08-13 23:03 ` Tejun Heo 2013-08-13 23:03 ` Tejun Heo
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