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Message-ID: <b7e5ce7837acad87b54fee5e30e0e6d0ea0b35ac.camel@gmx.de>
Subject: Re: [RFC v2 00/34] SLUB: reduce irq disabled scope and make it RT
 compatible
From:   Mike Galbraith <efault@gmx.de>
To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Vlastimil Babka <vbabka@suse.cz>
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>
Date:   Sun, 04 Jul 2021 07:37:53 +0200
In-Reply-To: <ca0474137c1e5a16a1215693298c9cd93218e24c.camel@gmx.de>
References: <20210609113903.1421-1-vbabka@suse.cz>
         <20210702182944.lqa7o2a25to6czju@linutronix.de>
         <891dc24e38106f8542f4c72831d52dc1a1863ae8.camel@gmx.de>
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On Sat, 2021-07-03 at 17:47 +0200, Mike Galbraith wrote:
> On Sat, 2021-07-03 at 09:24 +0200, Mike Galbraith wrote:
> > It also appears to be saying that there's something RT specific to
> > stare at in addition to the list_lock business.
>
> The what is ___slab_alloc() consuming 3.9% CPU in tip-rt-slub whereas
> it consumes < 1% in both tip-rt (sans slub patches) and tip-slub.
>
> The why remains to ponder.

Ignoring odd distribution in the profile (red herring whackable via
prefetch games), and removing perf/debug options from the picture, the
remaining RT specific cost is just that of forced slow path.  For
hackbench in my little box, it adds up to right at 3%.

	-Mike