diff mbox

[RFC,7/7] net: don't check for active hrtimer after adding it

Message ID a8994b5dda7599c0d8ce9f66aef40b8587acf691.1404888801.git.viresh.kumar@linaro.org
State New
Headers show

Commit Message

Viresh Kumar July 9, 2014, 6:55 a.m. UTC
hrtimer_start*() family never fails to enqueue a hrtimer to a clock-base. The
only special case is when the hrtimer was in past. If it is getting enqueued to
local CPUs's clock-base, we raise a softirq and exit, else we handle that on
next interrupt on remote CPU.

At several places in the kernel, we try to make sure if hrtimer was added
properly or not by calling hrtimer_active(), like:

	hrtimer_start(timer, expires, mode);
	if (hrtimer_active(timer)) {
		/* Added successfully */
	} else {
		/* Was added in the past */
	}

As hrtimer_start*() never fails, hrtimer_active() is guaranteed to return '1'.
So, there is no point calling hrtimer_active().

This patch updates net core to get this fixed.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
 net/core/pktgen.c | 2 --
 1 file changed, 2 deletions(-)

Comments

Chris Redpath July 9, 2014, 10:32 a.m. UTC | #1
Hi Viresh,

On 09/07/14 07:55, Viresh Kumar wrote:
> hrtimer_start*() family never fails to enqueue a hrtimer to a clock-base. The
> only special case is when the hrtimer was in past. If it is getting enqueued to
> local CPUs's clock-base, we raise a softirq and exit, else we handle that on
> next interrupt on remote CPU.
>
> At several places in the kernel, we try to make sure if hrtimer was added
> properly or not by calling hrtimer_active(), like:
>
> 	hrtimer_start(timer, expires, mode);
> 	if (hrtimer_active(timer)) {
> 		/* Added successfully */
> 	} else {
> 		/* Was added in the past */
> 	}
>
> As hrtimer_start*() never fails, hrtimer_active() is guaranteed to return '1'.
> So, there is no point calling hrtimer_active().
>
> This patch updates net core to get this fixed.
>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: netdev@vger.kernel.org
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
>   net/core/pktgen.c | 2 --
>   1 file changed, 2 deletions(-)
>
> diff --git a/net/core/pktgen.c b/net/core/pktgen.c
> index fc17a9d..f911acd 100644
> --- a/net/core/pktgen.c
> +++ b/net/core/pktgen.c
> @@ -2186,8 +2186,6 @@ static void spin(struct pktgen_dev *pkt_dev, ktime_t spin_until)
>   		do {
>   			set_current_state(TASK_INTERRUPTIBLE);
>   			hrtimer_start_expires(&t.timer, HRTIMER_MODE_ABS);
> -			if (!hrtimer_active(&t.timer))
> -				t.task = NULL;
>
>   			if (likely(t.task))
>   				schedule();

I think this if condition can also be removed. hrtimer_init_sleeper 
copies the supplied task_struct * to the timer, which in this case is 
'current'. The check is likely to be there in case of !active case you 
removed.

>

--Chris
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Viresh Kumar July 9, 2014, 10:44 a.m. UTC | #2
Hi Chris,

On 9 July 2014 16:02, Chris Redpath <Chris.Redpath@arm.com> wrote:

>> diff --git a/net/core/pktgen.c b/net/core/pktgen.c
>> index fc17a9d..f911acd 100644
>> --- a/net/core/pktgen.c
>> +++ b/net/core/pktgen.c
>> @@ -2186,8 +2186,6 @@ static void spin(struct pktgen_dev *pkt_dev, ktime_t
>> spin_until)
>>                 do {
>>                         set_current_state(TASK_INTERRUPTIBLE);
>>                         hrtimer_start_expires(&t.timer, HRTIMER_MODE_ABS);
>> -                       if (!hrtimer_active(&t.timer))
>> -                               t.task = NULL;
>>
>>                         if (likely(t.task))
>>                                 schedule();
>
>
> I think this if condition can also be removed. hrtimer_init_sleeper copies
> the supplied task_struct * to the timer, which in this case is 'current'.
> The check is likely to be there in case of !active case you removed.

Yeah, it looks like we can get rid of this. Also,

        } while (t.task && pkt_dev->running && !signal_pending(current));

is present in the closing "}" of do-while loop and probably we
don't need to check t.task here as well.

And this review comment applies to patch 2/7 as well:
hrtimer: don't check for active hrtimer after adding it

I would still wait for somebody to prove us wrong :), and will resend
it next week only.

Thanks.
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Chris Redpath July 9, 2014, 10:48 a.m. UTC | #3
On 09/07/14 11:44, Viresh Kumar wrote:
> Hi Chris,
>
> On 9 July 2014 16:02, Chris Redpath <Chris.Redpath@arm.com> wrote:
>
>>> diff --git a/net/core/pktgen.c b/net/core/pktgen.c
>>> index fc17a9d..f911acd 100644
>>> --- a/net/core/pktgen.c
>>> +++ b/net/core/pktgen.c
>>> @@ -2186,8 +2186,6 @@ static void spin(struct pktgen_dev *pkt_dev, ktime_t
>>> spin_until)
>>>                  do {
>>>                          set_current_state(TASK_INTERRUPTIBLE);
>>>                          hrtimer_start_expires(&t.timer, HRTIMER_MODE_ABS);
>>> -                       if (!hrtimer_active(&t.timer))
>>> -                               t.task = NULL;
>>>
>>>                          if (likely(t.task))
>>>                                  schedule();
>>
>>
>> I think this if condition can also be removed. hrtimer_init_sleeper copies
>> the supplied task_struct * to the timer, which in this case is 'current'.
>> The check is likely to be there in case of !active case you removed.
>
> Yeah, it looks like we can get rid of this. Also,
>
>          } while (t.task && pkt_dev->running && !signal_pending(current));
>
> is present in the closing "}" of do-while loop and probably we
> don't need to check t.task here as well.
>
> And this review comment applies to patch 2/7 as well:
> hrtimer: don't check for active hrtimer after adding it
>
> I would still wait for somebody to prove us wrong :), and will resend
> it next week only.
>
> Thanks.
>

Yeah, no worries. I just happened to read it and not knowing any of the 
APIs had to look up what is going on.

BTW, I *will* get back to you about that broadcast stuff when I get back 
to it myself. Other priorities at the moment again.

--Chris
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diff mbox

Patch

diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index fc17a9d..f911acd 100644
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -2186,8 +2186,6 @@  static void spin(struct pktgen_dev *pkt_dev, ktime_t spin_until)
 		do {
 			set_current_state(TASK_INTERRUPTIBLE);
 			hrtimer_start_expires(&t.timer, HRTIMER_MODE_ABS);
-			if (!hrtimer_active(&t.timer))
-				t.task = NULL;
 
 			if (likely(t.task))
 				schedule();