From: Kuan-Wei Chiu <visitorckw@gmail.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: libc-alpha@sourceware.org, adhemerval.zanella@linaro.org,
goldstein.w.n@gmail.com
Subject: Re: [PATCH] stdlib: Optimize number of calls to comparison function
Date: Tue, 5 Dec 2023 02:31:03 +0800 [thread overview]
Message-ID: <ZW4a52600gzaB5vx@visitorckw-System-Product-Name> (raw)
In-Reply-To: <87y1eaxtst.fsf@oldenburg.str.redhat.com>
On Mon, Dec 04, 2023 at 09:20:50AM +0100, Florian Weimer wrote:
> I think the factor in stdlib/tst-qsort5.c needs to be adjusted:
>
> /* This is an arbitrary factor which is true for the current
> implementation across a wide range of sizes. */
> TEST_VERIFY (factor <= 4.5);
>
It seems that the factor can be adjusted to around 3.5. I can send
another patch for this adjustment or resend it as a patch series.
> On the other hand, the heapsort code is not really expected to run at
> all in the current implementation because median-of-three quicksort
> usually avoids degenerating behavior. If this heapsort variant uses a
> number of comparisons that is competitive to quicksort, maybe we should
> use it instead? And use insertion sort for short arrays only.
>
This patch currently reduces the comparison count only in scenarios
where deep recursion results in a fallback to heapsort. According to
the referenced paper, beyond n >= 16000, the comparison count of
bottom-up heapsort is lower than that of median-of-three quicksort.
However, my concern is that quicksort typically exhibits better
locality of reference, making it more cache-friendly, while heapsort
lacks this advantage.
Best regards,
Kuan-Wei Chiu
next prev parent reply other threads:[~2023-12-04 18:31 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-02 21:48 Kuan-Wei Chiu
2023-12-04 8:20 ` Florian Weimer
2023-12-04 18:31 ` Kuan-Wei Chiu [this message]
2023-12-05 10:44 ` Florian Weimer
2023-12-05 20:00 ` Kuan-Wei Chiu
2023-12-05 20:35 ` Zack Weinberg
2023-12-06 10:21 ` Florian Weimer
2023-12-06 12:51 ` Adhemerval Zanella Netto
2023-12-17 15:42 ` Zack Weinberg
2023-12-17 15:55 ` Florian Weimer
2023-12-17 16:47 ` Kuan-Wei Chiu
2023-12-17 18:02 ` Florian Weimer
2023-12-05 3:22 ` [PATCH v2 0/2] stdlib: Optimize number of calls to comparison function in qsort Kuan-Wei Chiu
2023-12-05 3:22 ` [PATCH v2 1/2] " Kuan-Wei Chiu
2023-12-05 3:22 ` [PATCH v2 2/2] stdlib: Adjust the factor in tst-qsort5 Kuan-Wei Chiu
2024-02-16 7:08 ` [PATCH] stdlib: Optimize number of calls to comparison function Kuan-Wei Chiu
2024-03-27 19:45 ` Adhemerval Zanella Netto
2024-03-27 19:59 ` Kuan-Wei Chiu
2024-03-27 20:42 ` Adhemerval Zanella Netto
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