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From: ebiederm@xmission.com (Eric W. Biederman)
To: "Farnitano, Jarrett" <jmf@amazon.com>
Cc: "kexec@lists.infradead.org" <kexec@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] kexec: yield to scheduler when loading kimage segments
Date: Mon, 11 Jun 2018 19:45:11 -0500	[thread overview]
Message-ID: <87bmcgsui0.fsf@xmission.com> (raw)
In-Reply-To: <588FC7E2-C106-456A-81E7-A98F99F0E392@amazon.com> (Jarrett Farnitano's message of "Mon, 11 Jun 2018 23:47:46 +0000")

"Farnitano, Jarrett" <jmf@amazon.com> writes:

>> On 6/11/18, 4:00 PM, "Eric W. Biederman" <ebiederm@xmission.com> wrote:
>> 
>>     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.
>
> I did run into a practical problem. Hardware watchdogs on embedded
> systems can have short timers on the order of seconds. If the system
> is locked up for a few seconds with only a single core available, the
> watchdog may not be pet in a timely fashion. If this happens, the
> hardware watchdog will fire and reset the system.
>
> This really only becomes a problem when you are working with a single
> core, a decently sized initrd, and have a constrained hardware
> watchdog.

That would do it.

My foggy memory says this was not included back in the days where
cond_resched was spelled "if (need_resched) schedule();"  There were
concerns with spreading that too thin.  cond_resched in this path seems
as reasonable as anything.

Eric

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WARNING: multiple messages have this Message-ID (diff)
From: ebiederm@xmission.com (Eric W. Biederman)
To: "Farnitano\, Jarrett" <jmf@amazon.com>
Cc: "kexec\@lists.infradead.org" <kexec@lists.infradead.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] kexec: yield to scheduler when loading kimage segments
Date: Mon, 11 Jun 2018 19:45:11 -0500	[thread overview]
Message-ID: <87bmcgsui0.fsf@xmission.com> (raw)
In-Reply-To: <588FC7E2-C106-456A-81E7-A98F99F0E392@amazon.com> (Jarrett Farnitano's message of "Mon, 11 Jun 2018 23:47:46 +0000")

"Farnitano, Jarrett" <jmf@amazon.com> writes:

>> On 6/11/18, 4:00 PM, "Eric W. Biederman" <ebiederm@xmission.com> wrote:
>> 
>>     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.
>
> I did run into a practical problem. Hardware watchdogs on embedded
> systems can have short timers on the order of seconds. If the system
> is locked up for a few seconds with only a single core available, the
> watchdog may not be pet in a timely fashion. If this happens, the
> hardware watchdog will fire and reset the system.
>
> This really only becomes a problem when you are working with a single
> core, a decently sized initrd, and have a constrained hardware
> watchdog.

That would do it.

My foggy memory says this was not included back in the days where
cond_resched was spelled "if (need_resched) schedule();"  There were
concerns with spreading that too thin.  cond_resched in this path seems
as reasonable as anything.

Eric

  reply	other threads:[~2018-06-12  0:45 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-11 17:35 [PATCH] kexec: yield to scheduler when loading kimage segments Jarrett Farnitano
2018-06-11 17:35 ` Jarrett Farnitano
2018-06-11 22:59 ` Eric W. Biederman
2018-06-11 22:59   ` Eric W. Biederman
2018-06-11 23:47   ` Farnitano, Jarrett
2018-06-11 23:47     ` Farnitano, Jarrett
2018-06-12  0:45     ` Eric W. Biederman [this message]
2018-06-12  0:45       ` Eric W. Biederman
2018-06-12  0:45 ` Eric W. Biederman
2018-06-12  0:45   ` Eric W. Biederman

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