linux-kernel - Re: [PATCH] kexec: yield to scheduler when loading kimage segments

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Message-ID: <87po0xszdx.fsf@xmission.com>
Date:   Mon, 11 Jun 2018 17:59:38 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Jarrett Farnitano <jmf@...zon.com>
Cc:     kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kexec: yield to scheduler when loading kimage segments

Jarrett Farnitano <jmf@...zon.com> writes:

> Without yielding while loading kimage segments, a large initrd
> will block all other work on the CPU performing the load until
> it is completed. For example loading an initrd of 200MB on a
> low power single core system will lock up the system for a few
> seconds.
>
> To increase system responsiveness to other tasks at that time,
> call cond_resched() in both the crash kernel and normal kernel
> segment loading loops.

I remember years ago something like this was proposed and there was a
reason we did not include it.  I don't remember what that reason is
right now.  But I am reluctant to ack this until I remember.

Is there a practical problem with unresponsiveness?  You are talking
an embedded machine and rarely are there people in front of embedded
computers these days.

Eric

> Signed-off-by: Jarrett Farnitano <jmf@...zon.com>
> ---
>  kernel/kexec_core.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index 5616755..8ee07d6 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -783,6 +783,8 @@ static int kimage_load_normal_segment(struct kimage *image,
>  		else
>  			buf += mchunk;
>  		mbytes -= mchunk;
> +
> +		cond_resched();
>  	}
>  out:
>  	return result;
> @@ -847,6 +849,8 @@ static int kimage_load_crash_segment(struct kimage *image,
>  		else
>  			buf += mchunk;
>  		mbytes -= mchunk;
> +
> +		cond_resched();
>  	}
>  out:
>  	return result;