From: Vlastimil Babka <vbabka@suse.cz>
To: Eric Dumazet <edumazet@google.com>
Cc: Michal Hocko <mhocko@kernel.org>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: __GFP_REPEAT usage in fq_alloc_node
Date: Fri, 6 Jan 2017 17:55:23 +0100 [thread overview]
Message-ID: <97be60da-72df-ad8f-db03-03f01c392823@suse.cz> (raw)
In-Reply-To: <CANn89iLy2KMUu80KekhvO31G4uXr4B0K8zvGjhfyBBp9d_ncBg@mail.gmail.com>
On 01/06/2017 05:48 PM, Eric Dumazet wrote:
> On Fri, Jan 6, 2017 at 8:31 AM, Vlastimil Babka <vbabka@suse.cz> wrote:
>
>>
>> I wonder what's that cause of the penalty (when accessing the vmapped
>> area I suppose?) Is it higher risk of collisions cache misses within the
>> area, compared to consecutive physical adresses?
>
> I believe tests were done with 48 fq qdisc, each having 2^16 slots.
> So I had 48 blocs,of 524288 bytes.
>
> Trying a bit harder at setup time to get 128 consecutive pages got
> less TLB pressure.
Hmm that's rather surprising to me. TLB caches the page table lookups
and the PFN's of the physical pages it translates to shouldn't matter -
the page tables will look the same. With 128 consecutive pages could
manifest the reduced collision cache miss effect though.
> --
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next prev parent reply other threads:[~2017-01-06 16:55 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-06 15:20 __GFP_REPEAT usage in fq_alloc_node Michal Hocko
2017-01-06 15:39 ` Eric Dumazet
2017-01-06 16:07 ` Michal Hocko
2017-01-06 16:19 ` Michal Hocko
2017-01-07 3:33 ` [PATCH] net: use kvmalloc rather than open coded variant kbuild test robot
2017-01-07 9:19 ` Michal Hocko
2017-01-07 3:35 ` kbuild test robot
2017-01-09 10:22 ` __GFP_REPEAT usage in fq_alloc_node Michal Hocko
2017-01-09 16:00 ` Eric Dumazet
2017-01-09 17:45 ` Michal Hocko
2017-01-09 17:53 ` Eric Dumazet
2017-01-14 23:43 ` [PATCH] net_sched: use kvmalloc rather than opencoded variant kbuild test robot
2017-01-16 8:54 ` Michal Hocko
2017-01-06 16:31 ` __GFP_REPEAT usage in fq_alloc_node Vlastimil Babka
2017-01-06 16:48 ` Eric Dumazet
2017-01-06 16:50 ` Eric Dumazet
2017-01-06 16:55 ` Vlastimil Babka [this message]
2017-01-06 17:08 ` Eric Dumazet
2017-01-06 17:18 ` Vlastimil Babka
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