From: Kuan-Wei Chiu <visitorckw@gmail.com>
To: Yury Norov <yury.norov@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
mm-commits@vger.kernel.org, jserv@ccns.ncku.edu.tw,
n26122115@gs.ncku.edu.tw
Subject: Re: + bitops-optimize-fns-for-improved-performance.patch added to mm-nonmm-unstable branch
Date: Sat, 27 Apr 2024 13:33:55 +0800 [thread overview]
Message-ID: <ZiyOQ7RtG763rUSJ@visitorckw-System-Product-Name> (raw)
In-Reply-To: <CAAH8bW9o+d48_84mWXwYkVgMzY+__UxfBnuzauci4qgt1jFZ+Q@mail.gmail.com>
On Fri, Apr 26, 2024 at 12:48:48PM -0700, Yury Norov wrote:
> On Fri, Apr 26, 2024 at 12:08 PM Andrew Morton
> <akpm@linux-foundation.org> wrote:
> >
> >
> > The patch titled
> > Subject: bitops: optimize fns() for improved performance
> > has been added to the -mm mm-nonmm-unstable branch. Its filename is
> > bitops-optimize-fns-for-improved-performance.patch
> >
> > This patch will shortly appear at
> > https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/bitops-optimize-fns-for-improved-performance.patch
> >
> > This patch will later appear in the mm-nonmm-unstable branch at
> > git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> >
> > Before you just go and hit "reply", please:
> > a) Consider who else should be cc'ed
> > b) Prefer to cc a suitable mailing list as well
> > c) Ideally: find the original patch on the mailing list and do a
> > reply-to-all to that, adding suitable additional cc's
> >
> > *** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
> >
> > The -mm tree is included into linux-next via the mm-everything
> > branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> > and is updated there every 2-3 working days
> >
> > ------------------------------------------------------
> > From: Kuan-Wei Chiu <visitorckw@gmail.com>
> > Subject: bitops: optimize fns() for improved performance
> > Date: Fri, 26 Apr 2024 11:51:52 +0800
> >
> > The current fns() repeatedly uses __ffs() to find the index of the least
> > significant bit and then clears the corresponding bit using __clear_bit().
> > The method for clearing the least significant bit can be optimized by
> > using word &= word - 1 instead.
> >
> > Typically, the execution time of one __ffs() plus one __clear_bit() is
> > longer than that of a bitwise AND operation and a subtraction. To improve
> > performance, the loop for clearing the least significant bit has been
> > replaced with word &= word - 1, followed by a single __ffs() operation to
> > obtain the answer. This change reduces the number of __ffs() iterations
> > from n to just one, enhancing overall performance.
> >
> > The following microbenchmark data, conducted on my x86-64 machine, shows
> > the execution time (in microseconds) required for 1000000 test data
> > generated by get_random_u64() and executed by fns() under different values
> > of n:
> >
> > +-----+---------------+---------------+
> > | n | time_old | time_new |
> > +-----+---------------+---------------+
> > | 0 | 29194 | 25878 |
> > | 1 | 25510 | 25497 |
> > | 2 | 27836 | 25721 |
> > | 3 | 30140 | 25673 |
> > | 4 | 32569 | 25426 |
> > | 5 | 34792 | 25690 |
> > | 6 | 37117 | 25651 |
> > | 7 | 39742 | 25383 |
> > | 8 | 42360 | 25657 |
> > | 9 | 44672 | 25897 |
> > | 10 | 47237 | 25819 |
> > | 11 | 49884 | 26530 |
> > | 12 | 51864 | 26647 |
> > | 13 | 54265 | 28915 |
> > | 14 | 56440 | 28373 |
> > | 15 | 58839 | 28616 |
> > | 16 | 62383 | 29128 |
> > | 17 | 64257 | 30041 |
> > | 18 | 66805 | 29773 |
> > | 19 | 69368 | 33203 |
> > | 20 | 72942 | 33688 |
> > | 21 | 77006 | 34518 |
> > | 22 | 80926 | 34298 |
> > | 23 | 85723 | 35586 |
> > | 24 | 90324 | 36376 |
> > | 25 | 95992 | 37465 |
> > | 26 | 101101 | 37599 |
> > | 27 | 106520 | 37466 |
> > | 28 | 113287 | 38163 |
> > | 29 | 120552 | 38810 |
> > | 30 | 128040 | 39373 |
> > | 31 | 135624 | 40500 |
> > | 32 | 142580 | 40343 |
> > | 33 | 148915 | 40460 |
> > | 34 | 154005 | 41294 |
> > | 35 | 157996 | 41730 |
> > | 36 | 160806 | 41523 |
> > | 37 | 162975 | 42088 |
> > | 38 | 163426 | 41530 |
> > | 39 | 164872 | 41789 |
> > | 40 | 164477 | 42505 |
> > | 41 | 164758 | 41879 |
> > | 42 | 164182 | 41415 |
> > | 43 | 164842 | 42119 |
> > | 44 | 164881 | 42297 |
> > | 45 | 164870 | 42145 |
> > | 46 | 164673 | 42066 |
> > | 47 | 164616 | 42051 |
> > | 48 | 165055 | 41902 |
> > | 49 | 164847 | 41862 |
> > | 50 | 165171 | 41960 |
> > | 51 | 164851 | 42089 |
> > | 52 | 164763 | 41717 |
> > | 53 | 164635 | 42154 |
> > | 54 | 164757 | 41983 |
> > | 55 | 165095 | 41419 |
> > | 56 | 164641 | 42381 |
> > | 57 | 164601 | 41654 |
> > | 58 | 164864 | 41834 |
> > | 59 | 164594 | 41920 |
> > | 60 | 165207 | 42020 |
> > | 61 | 165056 | 41185 |
> > | 62 | 165160 | 41722 |
> > | 63 | 164923 | 41702 |
> > | 64 | 164777 | 41880 |
> > +-----+---------------+---------------+
>
> Hi Kuan-Wei,
>
> I didn't receive the original email for some reason...
> We've got a performance test for the function in find_bit_benchmark.
> Can you print before/after here?
>
> Thanks,
> Yury
>
Hi Yury,
Here are the benchmark results:
Before:
Start testing find_bit() with random-filled bitmap
[ 0.299085] fbcon: Taking over console
[ 0.299820] find_next_bit: 606286 ns, 164169 iterations
[ 0.300463] find_next_zero_bit: 641072 ns, 163512 iterations
[ 0.300996] find_last_bit: 531027 ns, 164169 iterations
[ 0.305233] find_nth_bit: 4235859 ns, 16454 iterations
[ 0.306434] find_first_bit: 1199357 ns, 16455 iterations
[ 0.321616] find_first_and_bit: 15179667 ns, 32869 iterations
[ 0.321917] find_next_and_bit: 298836 ns, 73875 iterations
[ 0.321918]
Start testing find_bit() with sparse bitmap
[ 0.321953] find_next_bit: 7931 ns, 656 iterations
[ 0.323201] find_next_zero_bit: 1246980 ns, 327025 iterations
[ 0.323210] find_last_bit: 8000 ns, 656 iterations
[ 0.324427] find_nth_bit: 1213161 ns, 655 iterations
[ 0.324813] find_first_bit: 384747 ns, 656 iterations
[ 0.324817] find_first_and_bit: 2220 ns, 1 iterations
[ 0.324820] find_next_and_bit: 1831 ns, 1 iterations
After:
Start testing find_bit() with random-filled bitmap
[ 0.305081] fbcon: Taking over console
[ 0.306126] find_next_bit: 854517 ns, 163960 iterations
[ 0.307041] find_next_zero_bit: 911725 ns, 163721 iterations
[ 0.307711] find_last_bit: 668261 ns, 163960 iterations
[ 0.311160] find_nth_bit: 3447530 ns, 16372 iterations
[ 0.312358] find_first_bit: 1196633 ns, 16373 iterations
[ 0.327191] find_first_and_bit: 14830129 ns, 32951 iterations
[ 0.327503] find_next_and_bit: 310560 ns, 73719 iterations
[ 0.327504]
Start testing find_bit() with sparse bitmap
[ 0.327539] find_next_bit: 7633 ns, 656 iterations
[ 0.328787] find_next_zero_bit: 1247398 ns, 327025 iterations
[ 0.328797] find_last_bit: 8425 ns, 656 iterations
[ 0.330034] find_nth_bit: 1234044 ns, 655 iterations
[ 0.330428] find_first_bit: 392086 ns, 656 iterations
[ 0.330431] find_first_and_bit: 1980 ns, 1 iterations
[ 0.330434] find_next_and_bit: 1831 ns, 1 iterations
Some benchmarks seem to have worsened after applying this patch.
However, unless I'm mistaken, the fns() changes should only affect the
results of find_nth_bit, while the others are just random fluctuations.
Should I include the above benchmark data in the commit message and
send a v2 patch?
Additionally, I apologize for you not receiving the email. I received
the following "Message not delivered" email, but I'm unsure if it's
related and what caused the error:
Date: Sat, 27 Apr 2024 04:29:04 +0000 (UTC)
From: do-not-reply@sophosemail.com
To: visitorckw@gmail.com
Subject: Undelivered Mail
This is an automated message from mail service of vivek.yagnik@sophosemail.com
⚠ Message not delivered
------------------ Message details ------------------
From: visitorckw@gmail.com
To: vivek.yagnik@sophosemail.com
Sent: 2024-04-27T04:29:03.000Z
Subject: [PATCH] bitops: Optimize fns() for improved performance
Failure reason: <vivek.yagnik@sophosemail.com>: host sophosemail-com.mail.protection.outlook.com[52.101.144.3]
+said: 451 4.4.4 Mail received as unauthenticated, incoming to a recipient domain configured in a hosted tenant
+which has no mail-enabled subscriptions. ATTR5 [MA1PEPF000072B2.INDPRD01.PROD.OUTLOOK.COM 2024-04-27T04:29:03.836Z
+08DC631634A0BBEB] (in reply to end of DATA command)
Regards,
Kuan-Wei
> > Link: https://lkml.kernel.org/r/20240426035152.956702-1-visitorckw@gmail.com
> > Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> > Cc: Ching-Chun (Jim) Huang <jserv@ccns.ncku.edu.tw>
> > Cc: Yury Norov <yury.norov@gmail.com>
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> > ---
> >
> > include/linux/bitops.h | 12 ++++--------
> > 1 file changed, 4 insertions(+), 8 deletions(-)
> >
> > --- a/include/linux/bitops.h~bitops-optimize-fns-for-improved-performance
> > +++ a/include/linux/bitops.h
> > @@ -254,16 +254,12 @@ static inline unsigned long __ffs64(u64
> > */
> > static inline unsigned long fns(unsigned long word, unsigned int n)
> > {
> > - unsigned int bit;
> > + unsigned int i;
> >
> > - while (word) {
> > - bit = __ffs(word);
> > - if (n-- == 0)
> > - return bit;
> > - __clear_bit(bit, &word);
> > - }
> > + for (i = 0; word && i < n; i++)
> > + word &= word - 1;
> >
> > - return BITS_PER_LONG;
> > + return word ? __ffs(word) : BITS_PER_LONG;
> > }
> >
> > /**
> > _
> >
> > Patches currently in -mm which might be from visitorckw@gmail.com are
> >
> > bitops-optimize-fns-for-improved-performance.patch
> >
next prev parent reply other threads:[~2024-04-27 5:33 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-26 19:08 + bitops-optimize-fns-for-improved-performance.patch added to mm-nonmm-unstable branch Andrew Morton
2024-04-26 19:48 ` Yury Norov
2024-04-27 5:33 ` Kuan-Wei Chiu [this message]
2024-04-28 16:08 ` Yury Norov
2024-04-29 8:05 ` Rasmus Villemoes
2024-04-29 15:40 ` Kuan-Wei Chiu
2024-04-29 16:34 ` Yury Norov
2024-04-29 17:06 ` Kuan-Wei Chiu
2024-04-29 16:26 ` Yury Norov
2024-04-29 15:31 ` Kuan-Wei Chiu
-- strict thread matches above, loose matches on Subject: below --
2024-05-02 15:18 Andrew Morton
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