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From: Richard Weinberger <richard@nod.at>
To: Kuan-Wei Chiu <visitorckw@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	 chengzhihao1 <chengzhihao1@huawei.com>,
	 Christoph Hellwig <hch@infradead.org>,
	 jserv <jserv@ccns.ncku.edu.tw>,
	eleanor15x <eleanor15x@gmail.com>,
	 marscheng <marscheng@google.com>,
	 linux-mtd <linux-mtd@lists.infradead.org>,
	 linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 1/2] ubifs: Remove unnecessary cond_resched() from list_sort() compare
Date: Wed, 25 Mar 2026 08:18:17 +0100 (CET)	[thread overview]
Message-ID: <2146783189.85721.1774423097193.JavaMail.zimbra@nod.at> (raw)
In-Reply-To: <20260320180938.1827148-2-visitorckw@gmail.com>

----- Ursprüngliche Mail -----
> Von: "Kuan-Wei Chiu" <visitorckw@gmail.com>
> An: "richard" <richard@nod.at>, "Andrew Morton" <akpm@linux-foundation.org>
> CC: "chengzhihao1" <chengzhihao1@huawei.com>, "Christoph Hellwig" <hch@infradead.org>, "jserv" <jserv@ccns.ncku.edu.tw>,
> "eleanor15x" <eleanor15x@gmail.com>, "marscheng" <marscheng@google.com>, "linux-mtd" <linux-mtd@lists.infradead.org>,
> "linux-kernel" <linux-kernel@vger.kernel.org>, "Kuan-Wei Chiu" <visitorckw@gmail.com>
> Gesendet: Freitag, 20. März 2026 19:09:37
> Betreff: [PATCH v3 1/2] ubifs: Remove unnecessary cond_resched() from list_sort() compare

> Historically, UBIFS embedded cond_resched() calls inside its
> list_sort() comparison callbacks (data_nodes_cmp, nondata_nodes_cmp,
> and replay_entries_cmp) to prevent soft lockups when sorting long
> lists.
> 
> However, further inspection by Richard Weinberger reveals that these
> compare functions are extremely lightweight and do not perform any
> blocking MTD I/O. Furthermore, the lists being sorted are strictly
> bounded in size:
> - In the GC case, the list contains at most the number of nodes that
>  fit into a single LEB.
> - In the replay case, the list spans across a few LEBs from the UBIFS
>  journal, amounting to at most a few thousand elements.
> 
> Since the compare functions are called a few thousand times at most,
> the overhead of frequent scheduling points is unjustified. Removing the
> cond_resched() calls simplifies the comparison logic and reduces
> unnecessary context switch checks during the sort.
> 
> Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>

Acked-by: Richard Weinberger <richard@nod.at>

Thanks,
//richard

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http://lists.infradead.org/mailman/listinfo/linux-mtd/

  parent reply	other threads:[~2026-03-25  7:18 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-03-20 18:09 [PATCH v3 0/2] lib/list_sort: Clean up list_sort() scheduling workarounds Kuan-Wei Chiu
2026-03-20 18:09 ` [PATCH v3 1/2] ubifs: Remove unnecessary cond_resched() from list_sort() compare Kuan-Wei Chiu
2026-03-21  2:06   ` Zhihao Cheng
2026-03-25  7:18   ` Richard Weinberger [this message]
2026-03-20 18:09 ` [PATCH v3 2/2] lib/list_sort: Remove dummy cmp() calls to speed up merge_final() Kuan-Wei Chiu
2026-03-25  5:44   ` Christoph Hellwig
2026-03-21  1:21 ` [PATCH v3 0/2] lib/list_sort: Clean up list_sort() scheduling workarounds Andrew Morton

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