[PATCH] f2fs: fix unnecessary periodic wakeup of discard thread when dev is busy

[PATCH] f2fs: fix unnecessary periodic wakeup of discard thread when dev is busy

[Sahitya Tummala]

When dev is busy, discard thread wake up timeout can be aligned with the
exact time that it needs to wait for dev to come out of busy. This helps
to avoid unnecessary periodic wakeups and thus save some power.

Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
---
 fs/f2fs/segment.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 8bcbb50..df14030 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -1379,6 +1379,8 @@ static int issue_discard_thread(void *data)
 	struct discard_policy dpolicy;
 	unsigned int wait_ms = DEF_MIN_DISCARD_ISSUE_TIME;
 	int issued;
+	unsigned long interval = sbi->interval_time[REQ_TIME] * HZ;
+	long delta;
 
 	set_freezable();
 
@@ -1410,7 +1412,11 @@ static int issue_discard_thread(void *data)
 			__wait_all_discard_cmd(sbi, &dpolicy);
 			wait_ms = dpolicy.min_interval;
 		} else if (issued == -1){
-			wait_ms = dpolicy.mid_interval;
+			delta = (sbi->last_time[REQ_TIME] + interval) - jiffies;
+			if (delta > 0)
+				wait_ms = jiffies_to_msecs(delta);
+			else
+				wait_ms = dpolicy.mid_interval;
 		} else {
 			wait_ms = dpolicy.max_interval;
 		}
-- 
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.

Re: [f2fs-dev] [PATCH] f2fs: fix unnecessary periodic wakeup of discard thread when dev is busy

[Chao Yu]

On 2018/8/31 17:39, Sahitya Tummala wrote:
> When dev is busy, discard thread wake up timeout can be aligned with the
> exact time that it needs to wait for dev to come out of busy. This helps
> to avoid unnecessary periodic wakeups and thus save some power.
> 
> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> ---
>  fs/f2fs/segment.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 8bcbb50..df14030 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1379,6 +1379,8 @@ static int issue_discard_thread(void *data)
>  	struct discard_policy dpolicy;
>  	unsigned int wait_ms = DEF_MIN_DISCARD_ISSUE_TIME;
>  	int issued;
> +	unsigned long interval = sbi->interval_time[REQ_TIME] * HZ;
> +	long delta;
>  
>  	set_freezable();
>  
> @@ -1410,7 +1412,11 @@ static int issue_discard_thread(void *data)
>  			__wait_all_discard_cmd(sbi, &dpolicy);
>  			wait_ms = dpolicy.min_interval;
>  		} else if (issued == -1){
> -			wait_ms = dpolicy.mid_interval;
> +			delta = (sbi->last_time[REQ_TIME] + interval) - jiffies;

I agree that we need to consider power consumption. One more consideration is
that discard thread may need different submission frequency comparing to garbage
collection thread, maybe a little fast, would it be better to split
sbi->interval_time[REQ_TIME] according to gc/discard type.

How do you think?

Thanks,

> +			if (delta > 0)
> +				wait_ms = jiffies_to_msecs(delta);
> +			else
> +				wait_ms = dpolicy.mid_interval;
>  		} else {
>  			wait_ms = dpolicy.max_interval;
>  		}
> 

Re: [PATCH] f2fs: fix unnecessary periodic wakeup of discard thread when dev is busy

[Sahitya Tummala]

On Sun, Sep 02, 2018 at 04:52:40PM +0800, Chao Yu wrote:
> On 2018/8/31 17:39, Sahitya Tummala wrote:
> > When dev is busy, discard thread wake up timeout can be aligned with the
> > exact time that it needs to wait for dev to come out of busy. This helps
> > to avoid unnecessary periodic wakeups and thus save some power.
> > 
> > Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> > ---
> >  fs/f2fs/segment.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index 8bcbb50..df14030 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -1379,6 +1379,8 @@ static int issue_discard_thread(void *data)
> >  	struct discard_policy dpolicy;
> >  	unsigned int wait_ms = DEF_MIN_DISCARD_ISSUE_TIME;
> >  	int issued;
> > +	unsigned long interval = sbi->interval_time[REQ_TIME] * HZ;
> > +	long delta;
> >  
> >  	set_freezable();
> >  
> > @@ -1410,7 +1412,11 @@ static int issue_discard_thread(void *data)
> >  			__wait_all_discard_cmd(sbi, &dpolicy);
> >  			wait_ms = dpolicy.min_interval;
> >  		} else if (issued == -1){
> > -			wait_ms = dpolicy.mid_interval;
> > +			delta = (sbi->last_time[REQ_TIME] + interval) - jiffies;
> 
> I agree that we need to consider power consumption. One more consideration is
> that discard thread may need different submission frequency comparing to garbage
> collection thread, maybe a little fast, would it be better to split
> sbi->interval_time[REQ_TIME] according to gc/discard type.
> 
> How do you think?
> 
> Thanks,
> 

Thanks for the review.

You mean when GC type is urgent? I see that for that case, the discard policy is
changed to DPOLICY_FORCE, which sets dpolicy->io_aware as false and hence,
cannot fall into this (issued == -1) case at all.

> > +			if (delta > 0)
> > +				wait_ms = jiffies_to_msecs(delta);
> > +			else
> > +				wait_ms = dpolicy.mid_interval;
> >  		} else {
> >  			wait_ms = dpolicy.max_interval;
> >  		}
> > 

-- 
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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Re: [f2fs-dev] [PATCH] f2fs: fix unnecessary periodic wakeup of discard thread when dev is busy

[Chao Yu]

On 2018/9/2 18:34, Sahitya Tummala wrote:
> On Sun, Sep 02, 2018 at 04:52:40PM +0800, Chao Yu wrote:
>> On 2018/8/31 17:39, Sahitya Tummala wrote:
>>> When dev is busy, discard thread wake up timeout can be aligned with the
>>> exact time that it needs to wait for dev to come out of busy. This helps
>>> to avoid unnecessary periodic wakeups and thus save some power.
>>>
>>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
>>> ---
>>>  fs/f2fs/segment.c | 8 +++++++-
>>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index 8bcbb50..df14030 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -1379,6 +1379,8 @@ static int issue_discard_thread(void *data)
>>>  	struct discard_policy dpolicy;
>>>  	unsigned int wait_ms = DEF_MIN_DISCARD_ISSUE_TIME;
>>>  	int issued;
>>> +	unsigned long interval = sbi->interval_time[REQ_TIME] * HZ;
>>> +	long delta;
>>>  
>>>  	set_freezable();
>>>  
>>> @@ -1410,7 +1412,11 @@ static int issue_discard_thread(void *data)
>>>  			__wait_all_discard_cmd(sbi, &dpolicy);
>>>  			wait_ms = dpolicy.min_interval;
>>>  		} else if (issued == -1){
>>> -			wait_ms = dpolicy.mid_interval;
>>> +			delta = (sbi->last_time[REQ_TIME] + interval) - jiffies;
>>
>> I agree that we need to consider power consumption. One more consideration is
>> that discard thread may need different submission frequency comparing to garbage
>> collection thread, maybe a little fast, would it be better to split
>> sbi->interval_time[REQ_TIME] according to gc/discard type.
>>
>> How do you think?
>>
>> Thanks,
>>
> 
> Thanks for the review.
> 
> You mean when GC type is urgent? I see that for that case, the discard policy is

Actually, I mean splitting sbi->interval_time[REQ_TIME] into:
- sbi->interval_time[GC_TIM] which can be used for GC thread.
- sbi->interval_time[DISCARD_TIME] which can be used for Discard thread.

Then we can configure sbi->interval_time[DISCARD_TIME] independently, and set
more suitable interval value for discard thread, since discard thread may need
to wake to submit discards more frequently.

I guess if we can accept above idea, it can be sent as another patch, so anyway,
I'm okay with your change. :)

Reviewed-by: Chao Yu <yuchao0@huawei.com>

Thanks,

> changed to DPOLICY_FORCE, which sets dpolicy->io_aware as false and hence,
> cannot fall into this (issued == -1) case at all.
> 
>>> +			if (delta > 0)
>>> +				wait_ms = jiffies_to_msecs(delta);
>>> +			else
>>> +				wait_ms = dpolicy.mid_interval;
>>>  		} else {
>>>  			wait_ms = dpolicy.max_interval;
>>>  		}
>>>
>