From: Vlastimil Babka <vbabka@suse.cz>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Christoph Lameter <cl@linux.com>,
David Rientjes <rientjes@google.com>,
Pekka Enberg <penberg@kernel.org>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Thomas Gleixner <tglx@linutronix.de>,
Mel Gorman <mgorman@techsingularity.net>,
Jesper Dangaard Brouer <brouer@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Jann Horn <jannh@google.com>
Subject: Re: [RFC v2 00/34] SLUB: reduce irq disabled scope and make it RT compatible
Date: Thu, 29 Jul 2021 16:17:26 +0200 [thread overview]
Message-ID: <627eddeb-3dc0-056e-ae07-f14c4b1a1b8e@suse.cz> (raw)
In-Reply-To: <20210729134939.iulryxjarhjmpugz@linutronix.de>
On 7/29/21 3:49 PM, Sebastian Andrzej Siewior wrote:
> now that I'm slowly catching up…
>
> On 2021-07-02 22:25:05 [+0200], Vlastimil Babka wrote:
>> > - perf_5.10 stat -r 10 hackbench -g200 -s 4096 -l500
>> > Old:
>> > | 464.967,20 msec task-clock # 27,220 CPUs utilized ( +- 0,16% )
>> > New:
>> > | 422.865,71 msec task-clock # 4,782 CPUs utilized ( +- 0,34% )
>>
>> The series shouldn't significantly change the memory allocator
>> interaction, though.
>> Seems there's less cycles, but more time elapsed, thus more sleeping -
>> is it locks becoming mutexes on RT?
>
> yes, most likely since the !RT parts are mostly unchanged.
>
>> My second guess - list_lock remains spinlock with my series, thus RT
>> mutex, but the current RT tree converts it to raw_spinlock. I'd hope
>> leaving that one as non-raw spinlock would still be much better for RT
>> goals, even if hackbench (which is AFAIK very slab intensive) throughput
>> regresses - hopefully not that much.
>
> Yes, the list_lock seems to be the case. I picked your
> slub-local-lock-v3r0 and changed the list_lock (+slab_lock()) to use
> raw_spinlock_t and disable interrupts and CPUs utilisation went to
> ~23CPUs (plus a bunch of warnings which probably made it a little slower
> again).
I forgot to point that out in the cover letter, but with v3 this change to
raw_spinlock_t is AFAICS no longer possible (at least with
CONFIG_SLUB_CPU_PARTIAL) because in put_cpu_partial() we now take the local_lock
and it can be called from get_partial_node() which takes the list_lock.
> The difference between a sleeping lock (spinlock_t) and a mutex is
> that we attempt not to preempt a task that acquired a spinlock_t even if
> it is running for some time and the scheduler would preempt it (like it
> would do if the task had a mutex acquired. These are the "lazy preempt"
> bits in the RT patch).
>
> By making the list_lock a raw_spinlock_t a lot of IRQ-flags dancing
> needs to be done as the page-allocator must be entered with enabled
> interrupts.
Hm but SLUB should never call the page allocator from under list_lock in my series?
> And then there is the possibility that you may need to free
> some memory even if you allocate memory which requires some extra steps
> on RT due to the IRQ-off part. All this vanishes by keeping list_lock a
> spinlock_t.
> The kernel-build test on /dev/shm remained unchanged so that is good.
> Unless there is a real-world use-case, that gets worse, I don't mind
> keeping the spinlock_t here. I haven't seen tglx complaining so far.
Good. IIRC hackbench is very close to being a slab microbenchmark, so
regressions there are expected, but should not translate to notable real world
regressions.
> Sebastian
>
next prev parent reply other threads:[~2021-07-29 14:17 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-09 11:38 Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 01/34] mm, slub: don't call flush_all() from list_locations() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 02/34] mm, slub: allocate private object map for sysfs listings Vlastimil Babka
2021-06-09 13:29 ` Christoph Lameter
2021-06-09 11:38 ` [RFC v2 03/34] mm, slub: allocate private object map for validate_slab_cache() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 04/34] mm, slub: don't disable irq for debug_check_no_locks_freed() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 05/34] mm, slub: remove redundant unfreeze_partials() from put_cpu_partial() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 06/34] mm, slub: unify cmpxchg_double_slab() and __cmpxchg_double_slab() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 07/34] mm, slub: extract get_partial() from new_slab_objects() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 08/34] mm, slub: dissolve new_slab_objects() into ___slab_alloc() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 09/34] mm, slub: return slab page from get_partial() and set c->page afterwards Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 10/34] mm, slub: restructure new page checks in ___slab_alloc() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 11/34] mm, slub: simplify kmem_cache_cpu and tid setup Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 12/34] mm, slub: move disabling/enabling irqs to ___slab_alloc() Vlastimil Babka
2021-07-06 4:38 ` Mike Galbraith
2021-06-09 11:38 ` [RFC v2 13/34] mm, slub: do initial checks in ___slab_alloc() with irqs enabled Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 14/34] mm, slub: move disabling irqs closer to get_partial() in ___slab_alloc() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 15/34] mm, slub: restore irqs around calling new_slab() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 16/34] mm, slub: validate slab from partial list or page allocator before making it cpu slab Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 17/34] mm, slub: check new pages with restored irqs Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 18/34] mm, slub: stop disabling irqs around get_partial() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 19/34] mm, slub: move reset of c->page and freelist out of deactivate_slab() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 20/34] mm, slub: make locking in deactivate_slab() irq-safe Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 21/34] mm, slub: call deactivate_slab() without disabling irqs Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 22/34] mm, slub: move irq control into unfreeze_partials() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 23/34] mm, slub: discard slabs in unfreeze_partials() without irqs disabled Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 24/34] mm, slub: detach whole partial list at once in unfreeze_partials() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 25/34] mm, slub: detach percpu partial list in unfreeze_partials() using this_cpu_cmpxchg() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 26/34] mm, slub: only disable irq with spin_lock in __unfreeze_partials() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 27/34] mm, slub: don't disable irqs in slub_cpu_dead() Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 28/34] mm, slab: make flush_slab() possible to call with irqs enabled Vlastimil Babka
2021-06-09 11:38 ` [RFC v2 29/34] mm: slub: Move flush_cpu_slab() invocations __free_slab() invocations out of IRQ context Vlastimil Babka
2021-06-09 22:29 ` Cyrill Gorcunov
2021-06-10 8:32 ` Vlastimil Babka
2021-06-10 8:36 ` Cyrill Gorcunov
2021-07-07 6:33 ` Hillf Danton
2021-06-09 11:38 ` [RFC v2 30/34] mm: slub: Make object_map_lock a raw_spinlock_t Vlastimil Babka
2021-06-09 11:39 ` [RFC v2 31/34] mm, slub: optionally save/restore irqs in slab_[un]lock()/ Vlastimil Babka
2021-07-02 12:17 ` Sebastian Andrzej Siewior
2021-06-09 11:39 ` [RFC v2 32/34] mm, slub: make slab_lock() disable irqs with PREEMPT_RT Vlastimil Babka
2021-06-09 11:39 ` [RFC v2 33/34] mm, slub: use migrate_disable() on PREEMPT_RT Vlastimil Babka
2021-06-14 11:07 ` Vlastimil Babka
2021-06-14 11:16 ` Sebastian Andrzej Siewior
2021-06-14 11:33 ` Vlastimil Babka
2021-06-14 12:54 ` Vlastimil Babka
2021-06-14 14:01 ` Sebastian Andrzej Siewior
2021-06-09 11:39 ` [RFC v2 34/34] mm, slub: convert kmem_cpu_slab protection to local_lock Vlastimil Babka
2021-06-14 9:49 ` [RFC v2 00/34] SLUB: reduce irq disabled scope and make it RT compatible Mel Gorman
2021-06-14 11:31 ` Mel Gorman
2021-06-14 11:10 ` Vlastimil Babka
2021-07-02 18:29 ` Sebastian Andrzej Siewior
2021-07-02 20:25 ` Vlastimil Babka
2021-07-29 13:49 ` Sebastian Andrzej Siewior
2021-07-29 14:17 ` Vlastimil Babka [this message]
2021-07-29 14:37 ` Sebastian Andrzej Siewior
2021-07-03 7:24 ` Mike Galbraith
2021-07-03 15:47 ` Mike Galbraith
2021-07-04 5:37 ` Mike Galbraith
2021-07-18 7:41 ` Vlastimil Babka
2021-07-18 8:29 ` Mike Galbraith
2021-07-18 12:09 ` Mike Galbraith
2021-07-05 16:00 ` Mike Galbraith
2021-07-06 17:56 ` Mike Galbraith
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