From: Yury <yury.norov@gmail.com>
To: Cassidy Burden <cburden@codeaurora.org>
Cc: akpm@linux-foundation.org, linux-arm-msm@vger.kernel.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Alexey Klimov <klimov.linux@gmail.com>,
"David S. Miller" <davem@davemloft.net>,
Daniel Borkmann <dborkman@redhat.com>,
Hannes Frederic Sowa <hannes@stressinduktion.org>,
Lai Jiangshan <laijs@cn.fujitsu.com>,
Mark Salter <msalter@redhat.com>,
AKASHI Takahiro <takahiro.akashi@linaro.org>,
Thomas Graf <tgraf@suug.ch>,
Valentin Rothberg <valentinrothberg@gmail.com>,
Chris Wilson <chris@chris-wilson.co.uk>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
linux@horizon.com
Subject: Re: [PATCH] lib: Make _find_next_bit helper function inline
Date: Wed, 29 Jul 2015 00:38:45 +0300 [thread overview]
Message-ID: <55B7F665.8050703@gmail.com> (raw)
In-Reply-To: <55B7F2C6.9010000@gmail.com>
On 29.07.2015 00:23, Yury wrote:
> On 28.07.2015 22:09, Cassidy Burden wrote:
>> I've tested Yury Norov's find_bit reimplementation with the
>> test_find_bit
>> module (https://lkml.org/lkml/2015/3/8/141) and measured about 35-40%
>> performance degradation on arm64 3.18 run with fixed CPU frequency.
>>
>> The performance degradation appears to be caused by the
>> helper function _find_next_bit. After inlining this function into
>> find_next_bit and find_next_zero_bit I get slightly better performance
>> than the old implementation:
>>
>> find_next_zero_bit find_next_bit
>> old new inline old new inline
>> 26 36 24 24 33 23
>> 25 36 24 24 33 23
>> 26 36 24 24 33 23
>> 25 36 24 24 33 23
>> 25 36 24 24 33 23
>> 25 37 24 24 33 23
>> 25 37 24 24 33 23
>> 25 37 24 24 33 23
>> 25 36 24 24 33 23
>> 25 37 24 24 33 23
>>
>> Signed-off-by: Cassidy Burden <cburden@codeaurora.org>
>> Cc: Alexey Klimov <klimov.linux@gmail.com>
>> Cc: David S. Miller <davem@davemloft.net>
>> Cc: Daniel Borkmann <dborkman@redhat.com>
>> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
>> Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
>> Cc: Mark Salter <msalter@redhat.com>
>> Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
>> Cc: Thomas Graf <tgraf@suug.ch>
>> Cc: Valentin Rothberg <valentinrothberg@gmail.com>
>> Cc: Chris Wilson <chris@chris-wilson.co.uk>
>> ---
>> lib/find_bit.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/lib/find_bit.c b/lib/find_bit.c
>> index 18072ea..d0e04f9 100644
>> --- a/lib/find_bit.c
>> +++ b/lib/find_bit.c
>> @@ -28,7 +28,7 @@
>> * find_next_zero_bit. The difference is the "invert" argument, which
>> * is XORed with each fetched word before searching it for one bits.
>> */
>> -static unsigned long _find_next_bit(const unsigned long *addr,
>> +static inline unsigned long _find_next_bit(const unsigned long *addr,
>> unsigned long nbits, unsigned long start, unsigned long
>> invert)
>> {
>> unsigned long tmp;
>
> Hi Cassidi,
>
> At first, I'm really surprised that there's no assembler implementation
> of find_bit routines for aarch64. Aarch32 has ones...
>
> I was thinking on inlining the helper, but decided not to do this....
>
> 1. Test is not too realistic. https://lkml.org/lkml/2015/2/1/224
> The typical usage pattern is to look for a single bit or range of bits.
> So in practice nobody calls find_next_bit thousand times.
>
> 2. Way more important to fit functions into as less cache lines as
> possible. https://lkml.org/lkml/2015/2/12/114
> In this case, inlining increases cache lines consumption almost twice...
>
> 3. Inlining prevents compiler from some other possible optimizations.
> It's
> probable that in real module compiler will inline callers of
> _find_next_bit,
> and final output will be better. I don't like to point out the
> compiler how
> it should do its work.
>
> Nevertheless, if this is your real case, and inlining helps, I'm OK
> with it.
>
> But I think, before/after for x86 is needed as well.
> And why don't you consider '__always_inline__'? Simple inline is only
> a hint and
> guarantees nothing.
(Sorry for typo in your name. Call me Yuri next time.)
Adding Rasmus and George to CC
next prev parent reply other threads:[~2015-07-28 21:38 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-28 19:09 [PATCH] lib: Make _find_next_bit helper function inline Cassidy Burden
2015-07-28 21:23 ` Yury
2015-07-28 21:38 ` Yury [this message]
2015-07-28 21:45 ` Andrew Morton
2015-07-29 13:30 ` Alexey Klimov
2015-07-29 20:40 ` Cassidy Burden
2015-08-23 22:53 ` Alexey Klimov
2015-08-29 15:15 ` Yury
2015-08-30 21:47 ` Rasmus Villemoes
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