From: Shreyas B Prabhu <shreyas@linux•vnet.ibm.com>
To: Daniel Lezcano <daniel.lezcano@linaro•org>, rjw@rjwysocki•net
Cc: linux-pm@vger•kernel.org, linuxppc-dev@lists•ozlabs.org,
anton@samba•org, mpe@ellerman•id.au, bsingharora@gmail•com,
David.Laight@ACULAB•COM, arnd@arndb•de,
Nicolas Pitre <nicolas.pitre@linaro•org>
Subject: Re: [PATCH v3] cpuidle: Fix last_residency division
Date: Wed, 29 Jun 2016 14:29:36 +0530 [thread overview]
Message-ID: <57738DF8.3000909@linux.vnet.ibm.com> (raw)
In-Reply-To: <57737AA1.7050201@linaro.org>
>>
>> +/*
>> + * Used for calculating last_residency in usec. Optimized for case
>> + * where last_residency in nsecs is < INT_MAX/2 by using faster
>> + * approximation. Approximated value has less than 1% error.
>> + */
>> +static inline int convert_nsec_to_usec(u64 nsec)
>> +{
>> + if (likely(nsec < INT_MAX / 2)) {
>
> UINT_MAX ?
I don't think I can use UINT_MAX here since usec += usec >> 5 can
overflow. Also using INT_MAX / 2 instead of INT_MAX since potentially
usec += usec >> 5 can be negative and usec >> 10 will retain the sign bit.
>
>> + int usec = (int)nsec;
>> +
>> + usec += usec >> 5;
>> + usec = usec >> 10;
>> + return usec;
>> + } else {
>> + u64 usec = div_u64(nsec, 1000);
>> +
>> + if (usec > INT_MAX)
>> + usec = INT_MAX;
>> + return (int)usec;
>> + }
>> +}
>
Thanks,
Shreyas
next prev parent reply other threads:[~2016-06-29 8:59 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-29 7:06 [PATCH v3] cpuidle: Fix last_residency division Shreyas B. Prabhu
2016-06-29 7:37 ` Daniel Lezcano
2016-06-29 8:59 ` Shreyas B Prabhu [this message]
2016-06-29 15:01 ` Nicolas Pitre
2016-06-29 15:52 ` Nicolas Pitre
2016-06-30 14:20 ` Shreyas B Prabhu
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