linux-kernel - Re: [PATCH 1/8] ntb_perf: Schedule based on time not on performance

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Date:	Mon, 13 Jun 2016 18:05:34 +0000
From:	"Jiang, Dave" <dave.jiang@...el.com>
To:	"Allen.Hubbe@....com" <Allen.Hubbe@....com>,
	"logang@...tatee.com" <logang@...tatee.com>,
	"jdmason@...zu.us" <jdmason@...zu.us>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"shuahkh@....samsung.com" <shuahkh@....samsung.com>,
	"sudipm.mukherjee@...il.com" <sudipm.mukherjee@...il.com>,
	"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
	"arnd@...db.de" <arnd@...db.de>,
	"linux-ntb@...glegroups.com" <linux-ntb@...glegroups.com>
Subject: Re: [PATCH 1/8] ntb_perf: Schedule based on time not on performance

On Fri, 2016-06-10 at 16:54 -0600, Logan Gunthorpe wrote:
> When debugging performance problems, if some issue causes the ntb
> hardware to be significantly slower than expected, ntb_perf will
> hang requiring a reboot because it only schedules once every 4GB.
> 
> Instead, schedule based on jiffies so it will not hang the CPU if
> the transfer is slow.
> 
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
Acked-by: Dave Jiang <dave.jiang@...el.com>

> ---
>  drivers/ntb/test/ntb_perf.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/ntb/test/ntb_perf.c
> b/drivers/ntb/test/ntb_perf.c
> index 4368519..5008ccf 100644
> --- a/drivers/ntb/test/ntb_perf.c
> +++ b/drivers/ntb/test/ntb_perf.c
> @@ -273,6 +273,7 @@ static int perf_move_data(struct pthr_ctx *pctx,
> char __iomem *dst, char *src,
>  	char __iomem *tmp = dst;
>  	u64 perf, diff_us;
>  	ktime_t kstart, kstop, kdiff;
> +	unsigned long last_sleep = jiffies;
>  
>  	chunks = div64_u64(win_size, buf_size);
>  	total_chunks = div64_u64(total, buf_size);
> @@ -288,8 +289,9 @@ static int perf_move_data(struct pthr_ctx *pctx,
> char __iomem *dst, char *src,
>  		} else
>  			tmp += buf_size;
>  
> -		/* Probably should schedule every 4GB to prevent
> soft hang. */
> -		if (((copied % SZ_4G) == 0) && !use_dma) {
> +		/* Probably should schedule every 5s to prevent soft
> hang. */
> +		if (unlikely((jiffies - last_sleep) > 5 * HZ)) {
> +			last_sleep = jiffies;
>  			set_current_state(TASK_INTERRUPTIBLE);
>  			schedule_timeout(1);
>  		}
> -- 
> 2.1.4
>