Re: [PATCH V2 04/16] block, bfq: modify the peak-rate estimator

[Paolo Valente]

> Il giorno 04 apr 2017, alle ore 17:28, Bart Van Assche 
>  ha scritto:
> 
> On Tue, 2017-04-04 at 12:42 +0200, Paolo Valente wrote:
>>> Il giorno 31 mar 2017, alle ore 17:31, Bart Van Assche 
>>>  ha scritto:
>>> 
>>> On Fri, 2017-03-31 at 14:47 +0200, Paolo Valente wrote:
 +   delta_ktime = ktime_get();
 +   delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
 +   delta_usecs = ktime_to_us(delta_ktime);
>>> 
>>> This patch changes the type of the variable in which the result of 
>>> ktime_to_us()
>>> is stored from u64 into u32 and next compares that result with LONG_MAX. 
>>> Since
>>> ktime_to_us() returns a signed 64-bit number, are you sure you want to 
>>> store that
>>> result in a 32-bit variable? If ktime_to_us() would e.g. return 
>>> 0x0100
>>> or 0x10100 then the assignment will truncate these numbers to 0x100.
>> 
>> The instruction above the assignment you highlight stores in
>> delta_ktime the difference between 'now' and the last budget start.
>> The latter may have happened at most about 100 ms before 'now'.  So
>> there should be no overflow issue.
> 
> Hello Paolo,
> 
> Please double check the following code: if (delta_usecs < 1000 || delta_usecs 
> >= LONG_MAX)
> Since delta_usecs is a 32-bit variable and LONG_MAX a 64-bit constant on 
> 64-bit systems
> I'm not sure that code will do what it is intended to do.
> 

Yes, sorry. Actually, it never occurred to me to see that extra condition to 
hold over the last eight years on 32-bit systems. So I think I will just remove 
it. Unless Fabio, who inserted that condition several years ago, has something 
to say.

Thanks,
Paolo

> Thanks,
> 
> Bart.

Re: [PATCH V2 04/16] block, bfq: modify the peak-rate estimator

[Paolo Valente]

> Il giorno 04 apr 2017, alle ore 17:28, Bart Van Assche 
>  ha scritto:
> 
> On Tue, 2017-04-04 at 12:42 +0200, Paolo Valente wrote:
>>> Il giorno 31 mar 2017, alle ore 17:31, Bart Van Assche 
>>>  ha scritto:
>>> 
>>> On Fri, 2017-03-31 at 14:47 +0200, Paolo Valente wrote:
 +   delta_ktime = ktime_get();
 +   delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
 +   delta_usecs = ktime_to_us(delta_ktime);
>>> 
>>> This patch changes the type of the variable in which the result of 
>>> ktime_to_us()
>>> is stored from u64 into u32 and next compares that result with LONG_MAX. 
>>> Since
>>> ktime_to_us() returns a signed 64-bit number, are you sure you want to 
>>> store that
>>> result in a 32-bit variable? If ktime_to_us() would e.g. return 
>>> 0x0100
>>> or 0x10100 then the assignment will truncate these numbers to 0x100.
>> 
>> The instruction above the assignment you highlight stores in
>> delta_ktime the difference between 'now' and the last budget start.
>> The latter may have happened at most about 100 ms before 'now'.  So
>> there should be no overflow issue.
> 
> Hello Paolo,
> 
> Please double check the following code: if (delta_usecs < 1000 || delta_usecs 
> >= LONG_MAX)
> Since delta_usecs is a 32-bit variable and LONG_MAX a 64-bit constant on 
> 64-bit systems
> I'm not sure that code will do what it is intended to do.
> 

Yes, sorry. Actually, it never occurred to me to see that extra condition to 
hold over the last eight years on 32-bit systems. So I think I will just remove 
it. Unless Fabio, who inserted that condition several years ago, has something 
to say.

Thanks,
Paolo

> Thanks,
> 
> Bart.

Re: [PATCH V2 04/16] block, bfq: modify the peak-rate estimator

[Bart Van Assche]

On Tue, 2017-04-04 at 12:42 +0200, Paolo Valente wrote:
> > Il giorno 31 mar 2017, alle ore 17:31, Bart Van Assche 
> >  ha scritto:
> > 
> > On Fri, 2017-03-31 at 14:47 +0200, Paolo Valente wrote:
> > > +   delta_ktime = ktime_get();
> > > +   delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
> > > +   delta_usecs = ktime_to_us(delta_ktime);
> > 
> > This patch changes the type of the variable in which the result of 
> > ktime_to_us()
> > is stored from u64 into u32 and next compares that result with LONG_MAX. 
> > Since
> > ktime_to_us() returns a signed 64-bit number, are you sure you want to 
> > store that
> > result in a 32-bit variable? If ktime_to_us() would e.g. return 
> > 0x0100
> > or 0x10100 then the assignment will truncate these numbers to 0x100.
> 
> The instruction above the assignment you highlight stores in
> delta_ktime the difference between 'now' and the last budget start.
> The latter may have happened at most about 100 ms before 'now'.  So
> there should be no overflow issue.

Hello Paolo,

Please double check the following code: if (delta_usecs < 1000 || delta_usecs 
>= LONG_MAX)
Since delta_usecs is a 32-bit variable and LONG_MAX a 64-bit constant on 64-bit 
systems
I'm not sure that code will do what it is intended to do.

Thanks,

Bart.

Re: [PATCH V2 04/16] block, bfq: modify the peak-rate estimator

[Bart Van Assche]

On Tue, 2017-04-04 at 12:42 +0200, Paolo Valente wrote:
> > Il giorno 31 mar 2017, alle ore 17:31, Bart Van Assche 
> >  ha scritto:
> > 
> > On Fri, 2017-03-31 at 14:47 +0200, Paolo Valente wrote:
> > > +   delta_ktime = ktime_get();
> > > +   delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
> > > +   delta_usecs = ktime_to_us(delta_ktime);
> > 
> > This patch changes the type of the variable in which the result of 
> > ktime_to_us()
> > is stored from u64 into u32 and next compares that result with LONG_MAX. 
> > Since
> > ktime_to_us() returns a signed 64-bit number, are you sure you want to 
> > store that
> > result in a 32-bit variable? If ktime_to_us() would e.g. return 
> > 0x0100
> > or 0x10100 then the assignment will truncate these numbers to 0x100.
> 
> The instruction above the assignment you highlight stores in
> delta_ktime the difference between 'now' and the last budget start.
> The latter may have happened at most about 100 ms before 'now'.  So
> there should be no overflow issue.

Hello Paolo,

Please double check the following code: if (delta_usecs < 1000 || delta_usecs 
>= LONG_MAX)
Since delta_usecs is a 32-bit variable and LONG_MAX a 64-bit constant on 64-bit 
systems
I'm not sure that code will do what it is intended to do.

Thanks,

Bart.

Re: [PATCH V2 04/16] block, bfq: modify the peak-rate estimator

[Paolo Valente]

> Il giorno 31 mar 2017, alle ore 17:31, Bart Van Assche 
>  ha scritto:
> 
> On Fri, 2017-03-31 at 14:47 +0200, Paolo Valente wrote:
>> -static bool bfq_update_peak_rate(struct bfq_data *bfqd, struct bfq_queue 
>> *bfqq,
>> -bool compensate)
>> +static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq,
>> +bool compensate, enum bfqq_expiration 
>> reason,
>> +unsigned long *delta_ms)
>>  {
>> -   u64 bw, usecs, expected, timeout;
>> -   ktime_t delta;
>> -   int update = 0;
>> +   ktime_t delta_ktime;
>> +   u32 delta_usecs;
>> +   bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */
>>  
>> -   if (!bfq_bfqq_sync(bfqq) || bfq_bfqq_budget_new(bfqq))
>> +   if (!bfq_bfqq_sync(bfqq))
>> return false;
>>  
>> if (compensate)
>> -   delta = bfqd->last_idling_start;
>> +   delta_ktime = bfqd->last_idling_start;
>> else
>> -   delta = ktime_get();
>> -   delta = ktime_sub(delta, bfqd->last_budget_start);
>> -   usecs = ktime_to_us(delta);
>> -
>> -   /* Don't trust short/unrealistic values. */
>> -   if (usecs < 100 || usecs >= LONG_MAX)
>> -   return false;
>> -
>> -   /*
>> -* Calculate the bandwidth for the last slice.  We use a 64 bit
>> -* value to store the peak rate, in sectors per usec in fixed
>> -* point math.  We do so to have enough precision in the estimate
>> -* and to avoid overflows.
>> -*/
>> -   bw = (u64)bfqq->entity.service << BFQ_RATE_SHIFT;
>> -   do_div(bw, (unsigned long)usecs);
>> +   delta_ktime = ktime_get();
>> +   delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
>> +   delta_usecs = ktime_to_us(delta_ktime);
>> +
> 
> This patch changes the type of the variable in which the result of 
> ktime_to_us()
> is stored from u64 into u32 and next compares that result with LONG_MAX. Since
> ktime_to_us() returns a signed 64-bit number, are you sure you want to store 
> that
> result in a 32-bit variable? If ktime_to_us() would e.g. return 
> 0x0100
> or 0x10100 then the assignment will truncate these numbers to 0x100.
> 

The instruction above the assignment you highlight stores in
delta_ktime the difference between 'now' and the last budget start.
The latter may have happened at most about 100 ms before 'now'.  So
there should be no overflow issue.

Thanks,
Paolo

> Bart.

Re: [PATCH V2 04/16] block, bfq: modify the peak-rate estimator

[Paolo Valente]

> Il giorno 31 mar 2017, alle ore 17:31, Bart Van Assche 
>  ha scritto:
> 
> On Fri, 2017-03-31 at 14:47 +0200, Paolo Valente wrote:
>> -static bool bfq_update_peak_rate(struct bfq_data *bfqd, struct bfq_queue 
>> *bfqq,
>> -bool compensate)
>> +static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq,
>> +bool compensate, enum bfqq_expiration 
>> reason,
>> +unsigned long *delta_ms)
>>  {
>> -   u64 bw, usecs, expected, timeout;
>> -   ktime_t delta;
>> -   int update = 0;
>> +   ktime_t delta_ktime;
>> +   u32 delta_usecs;
>> +   bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */
>>  
>> -   if (!bfq_bfqq_sync(bfqq) || bfq_bfqq_budget_new(bfqq))
>> +   if (!bfq_bfqq_sync(bfqq))
>> return false;
>>  
>> if (compensate)
>> -   delta = bfqd->last_idling_start;
>> +   delta_ktime = bfqd->last_idling_start;
>> else
>> -   delta = ktime_get();
>> -   delta = ktime_sub(delta, bfqd->last_budget_start);
>> -   usecs = ktime_to_us(delta);
>> -
>> -   /* Don't trust short/unrealistic values. */
>> -   if (usecs < 100 || usecs >= LONG_MAX)
>> -   return false;
>> -
>> -   /*
>> -* Calculate the bandwidth for the last slice.  We use a 64 bit
>> -* value to store the peak rate, in sectors per usec in fixed
>> -* point math.  We do so to have enough precision in the estimate
>> -* and to avoid overflows.
>> -*/
>> -   bw = (u64)bfqq->entity.service << BFQ_RATE_SHIFT;
>> -   do_div(bw, (unsigned long)usecs);
>> +   delta_ktime = ktime_get();
>> +   delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
>> +   delta_usecs = ktime_to_us(delta_ktime);
>> +
> 
> This patch changes the type of the variable in which the result of 
> ktime_to_us()
> is stored from u64 into u32 and next compares that result with LONG_MAX. Since
> ktime_to_us() returns a signed 64-bit number, are you sure you want to store 
> that
> result in a 32-bit variable? If ktime_to_us() would e.g. return 
> 0x0100
> or 0x10100 then the assignment will truncate these numbers to 0x100.
> 

The instruction above the assignment you highlight stores in
delta_ktime the difference between 'now' and the last budget start.
The latter may have happened at most about 100 ms before 'now'.  So
there should be no overflow issue.

Thanks,
Paolo

> Bart.

Re: [PATCH V2 04/16] block, bfq: modify the peak-rate estimator

[Bart Van Assche]

On Fri, 2017-03-31 at 14:47 +0200, Paolo Valente wrote:
> -static bool bfq_update_peak_rate(struct bfq_data *bfqd, struct bfq_queue 
> *bfqq,
> -    bool compensate)
> +static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq,
> +    bool compensate, enum bfqq_expiration reason,
> +    unsigned long *delta_ms)
>  {
> -   u64 bw, usecs, expected, timeout;
> -   ktime_t delta;
> -   int update = 0;
> +   ktime_t delta_ktime;
> +   u32 delta_usecs;
> +   bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */
>  
> -   if (!bfq_bfqq_sync(bfqq) || bfq_bfqq_budget_new(bfqq))
> +   if (!bfq_bfqq_sync(bfqq))
> return false;
>  
> if (compensate)
> -   delta = bfqd->last_idling_start;
> +   delta_ktime = bfqd->last_idling_start;
> else
> -   delta = ktime_get();
> -   delta = ktime_sub(delta, bfqd->last_budget_start);
> -   usecs = ktime_to_us(delta);
> -
> -   /* Don't trust short/unrealistic values. */
> -   if (usecs < 100 || usecs >= LONG_MAX)
> -   return false;
> -
> -   /*
> -    * Calculate the bandwidth for the last slice.  We use a 64 bit
> -    * value to store the peak rate, in sectors per usec in fixed
> -    * point math.  We do so to have enough precision in the estimate
> -    * and to avoid overflows.
> -    */
> -   bw = (u64)bfqq->entity.service << BFQ_RATE_SHIFT;
> -   do_div(bw, (unsigned long)usecs);
> +   delta_ktime = ktime_get();
> +   delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
> +   delta_usecs = ktime_to_us(delta_ktime);
> +

This patch changes the type of the variable in which the result of ktime_to_us()
is stored from u64 into u32 and next compares that result with LONG_MAX. Since
ktime_to_us() returns a signed 64-bit number, are you sure you want to store 
that
result in a 32-bit variable? If ktime_to_us() would e.g. return 
0x0100
or 0x10100 then the assignment will truncate these numbers to 0x100.

Bart.

Re: [PATCH V2 04/16] block, bfq: modify the peak-rate estimator

[Bart Van Assche]

On Fri, 2017-03-31 at 14:47 +0200, Paolo Valente wrote:
> -static bool bfq_update_peak_rate(struct bfq_data *bfqd, struct bfq_queue 
> *bfqq,
> -    bool compensate)
> +static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq,
> +    bool compensate, enum bfqq_expiration reason,
> +    unsigned long *delta_ms)
>  {
> -   u64 bw, usecs, expected, timeout;
> -   ktime_t delta;
> -   int update = 0;
> +   ktime_t delta_ktime;
> +   u32 delta_usecs;
> +   bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */
>  
> -   if (!bfq_bfqq_sync(bfqq) || bfq_bfqq_budget_new(bfqq))
> +   if (!bfq_bfqq_sync(bfqq))
> return false;
>  
> if (compensate)
> -   delta = bfqd->last_idling_start;
> +   delta_ktime = bfqd->last_idling_start;
> else
> -   delta = ktime_get();
> -   delta = ktime_sub(delta, bfqd->last_budget_start);
> -   usecs = ktime_to_us(delta);
> -
> -   /* Don't trust short/unrealistic values. */
> -   if (usecs < 100 || usecs >= LONG_MAX)
> -   return false;
> -
> -   /*
> -    * Calculate the bandwidth for the last slice.  We use a 64 bit
> -    * value to store the peak rate, in sectors per usec in fixed
> -    * point math.  We do so to have enough precision in the estimate
> -    * and to avoid overflows.
> -    */
> -   bw = (u64)bfqq->entity.service << BFQ_RATE_SHIFT;
> -   do_div(bw, (unsigned long)usecs);
> +   delta_ktime = ktime_get();
> +   delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
> +   delta_usecs = ktime_to_us(delta_ktime);
> +

This patch changes the type of the variable in which the result of ktime_to_us()
is stored from u64 into u32 and next compares that result with LONG_MAX. Since
ktime_to_us() returns a signed 64-bit number, are you sure you want to store 
that
result in a 32-bit variable? If ktime_to_us() would e.g. return 
0x0100
or 0x10100 then the assignment will truncate these numbers to 0x100.

Bart.