linux-kernel - Re: [PATCH 4.19 012/106] ipmi_si: Only schedule continuously in the thread in maintenance mode

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Date:   Tue, 8 Oct 2019 11:49:15 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Corey Minyard <cminyard@...sta.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 012/106] ipmi_si: Only schedule continuously in the
 thread in maintenance mode

Hi!

> @@ -1013,11 +1016,20 @@ static int ipmi_thread(void *data)
>  		spin_unlock_irqrestore(&(smi_info->si_lock), flags);
>  		busy_wait = ipmi_thread_busy_wait(smi_result, smi_info,
>  						  &busy_until);
> -		if (smi_result == SI_SM_CALL_WITHOUT_DELAY)
> +		if (smi_result == SI_SM_CALL_WITHOUT_DELAY) {
>  			; /* do nothing */
> -		else if (smi_result == SI_SM_CALL_WITH_DELAY && busy_wait)
> -			schedule();
> -		else if (smi_result == SI_SM_IDLE) {
> +		} else if (smi_result == SI_SM_CALL_WITH_DELAY && busy_wait) {
> +			/*
> +			 * In maintenance mode we run as fast as
> +			 * possible to allow firmware updates to
> +			 * complete as fast as possible, but normally
> +			 * don't bang on the scheduler.
> +			 */
> +			if (smi_info->in_maintenance_mode)
> +				schedule();
> +			else
> +				usleep_range(100, 200);
> +		} else if (smi_result == SI_SM_IDLE) {

This is quite crazy code. usleep() will need to do magic with high
resolution timers to provide 200usec sleep... when all you want to do
is unload the scheduler.

cond_resched() should be okay to call in a loop, can the code use that
instead?

Best regards,
									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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