linux-kernel - Re: [PATCH] KUnit: memcpy: add benchmark

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Message-Id: <20260129152035.1fbdddb214c75875b67ba5b9@linux-foundation.org>
Date: Thu, 29 Jan 2026 15:20:35 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Matteo Croce <technoboy85@...il.com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KUnit: memcpy: add benchmark

On Thu, 29 Jan 2026 01:43:28 +0100 Matteo Croce <technoboy85@...il.com> wrote:

> Add optional benchmarks for memcpy() and memmove() functions.
> Each benchmark is run twice: first with buffers aligned and then with
> buffers unaligned, to spot unaligned accesses on platforms where they
> have a noticeable performance impact.
> 
> ...
>
> +static int memcpy_bench_align(struct kunit *test, bool unalign)
> +{
> +	u64 start, end, total_ns = 0;
> +	char *buf1;
> +	char *buf2;
> +	int ret = 0;
> +
> +	buf1 = kzalloc(COPY_SIZE, GFP_KERNEL);
> +	if (!buf1)
> +		return -ENOMEM;
> +
> +	buf2 = kzalloc(COPY_SIZE, GFP_KERNEL);
> +	if (!buf2) {
> +		ret = -ENOMEM;
> +		goto out_free;
> +	}
> +
> +	preempt_disable();
> +	for (int i = 0; i < COPIES_NUM; i++) {
> +		start = ktime_get_ns();
> +		memcpy(buf1 + unalign, buf2, COPY_SIZE - unalign);
> +		end = ktime_get_ns();
> +		total_ns += end - start;
> +		cond_resched();

Is cond_resched() inside preempt_disable() actually legal?

Might be, but it doesn't make a lot of sense, does it?

> +	}
> +	preempt_enable();
> +