Re: [PATCH] Provide u64 version of jiffies_to_usecs() in kernel/tsacct.c - Kernel

This is a discussion on Re: [PATCH] Provide u64 version of jiffies_to_usecs() in kernel/tsacct.c - Kernel ; It's possible that the values used in and returned from jiffies_to_usecs() are incorrect because of truncation when variables of type u64 are involved. So a function specific to that type is used instead. This version implements a correction to jiffies_64_to_usecs() ...

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Thread: Re: [PATCH] Provide u64 version of jiffies_to_usecs() in kernel/tsacct.c

  1. Re: [PATCH] Provide u64 version of jiffies_to_usecs() in kernel/tsacct.c

    It's possible that the values used in and returned from jiffies_to_usecs() are
    incorrect because of truncation when variables of type u64 are involved. So a
    function specific to that type is used instead.

    This version implements a correction to jiffies_64_to_usecs() based on feedback
    from Randy Dunlap.

    Diff'd against: linux/kernel/git/torvalds/linux-2.6.git

    Signed-off-by: Jonathan Lim

    --- a/include/linux/jiffies.h Thu Feb 14 18:04:14 PST 2008
    +++ b/include/linux/jiffies.h Thu Feb 14 18:07:17 PST 2008
    @@ -42,7 +42,7 @@
    /* LATCH is used in the interval timer and ftape setup. */
    #define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ) /* For divider */

    -/* Suppose we want to devide two numbers NOM and DEN: NOM/DEN, then we can
    +/* Suppose we want to divide two numbers NOM and DEN: NOM/DEN, then we can
    * improve accuracy by shifting LSH bits, hence calculating:
    * (NOM << LSH) / DEN
    * This however means trouble for large NOM, because (NOM << LSH) may no
    @@ -204,7 +204,7 @@ extern unsigned long preset_lpj;
    * operator if the result is a long long AND at least one of the
    * operands is cast to long long (usually just prior to the "*" so as
    * not to confuse it into thinking it really has a 64-bit operand,
    - * which, buy the way, it can do, but it takes more code and at least 2
    + * which, by the way, it can do, but it takes more code and at least 2
    * mpys).

    * We also need to be aware that one second in nanoseconds is only a
    @@ -269,6 +269,7 @@ extern unsigned long preset_lpj;
    */
    extern unsigned int jiffies_to_msecs(const unsigned long j);
    extern unsigned int jiffies_to_usecs(const unsigned long j);
    +extern u64 jiffies_64_to_usecs(const u64 j);
    extern unsigned long msecs_to_jiffies(const unsigned int m);
    extern unsigned long usecs_to_jiffies(const unsigned int u);
    extern unsigned long timespec_to_jiffies(const struct timespec *value);
    --- a/kernel/time.c Thu Feb 14 18:05:12 PST 2008
    +++ b/kernel/time.c Mon Feb 25 14:22:27 PST 2008
    @@ -38,6 +38,7 @@

    #include
    #include
    +#include

    #include "timeconst.h"

    @@ -267,6 +268,12 @@ unsigned int inline jiffies_to_usecs(con
    #endif
    }
    EXPORT_SYMBOL(jiffies_to_usecs);
    +
    +u64 jiffies_64_to_usecs(const u64 j)
    +{
    + return div64_64(j*HZ_TO_USEC_NUM + HZ_TO_USEC_DEN-1, HZ_TO_USEC_DEN);
    +}
    +EXPORT_SYMBOL(jiffies_64_to_usecs);

    /**
    * timespec_trunc - Truncate timespec to a granularity
    --- a/kernel/tsacct.c Thu Feb 14 18:06:17 PST 2008
    +++ b/kernel/tsacct.c Thu Feb 14 18:08:47 PST 2008
    @@ -85,8 +85,8 @@ void xacct_add_tsk(struct taskstats *sta
    struct mm_struct *mm;

    /* convert pages-jiffies to Mbyte-usec */
    - stats->coremem = jiffies_to_usecs(p->acct_rss_mem1) * PAGE_SIZE / MB;
    - stats->virtmem = jiffies_to_usecs(p->acct_vm_mem1) * PAGE_SIZE / MB;
    + stats->coremem = jiffies_64_to_usecs(p->acct_rss_mem1) * PAGE_SIZE / MB;
    + stats->virtmem = jiffies_64_to_usecs(p->acct_vm_mem1) * PAGE_SIZE / MB;
    mm = get_task_mm(p);
    if (mm) {
    /* adjust to KB unit */
    --
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  2. Re: [PATCH] Provide u64 version of jiffies_to_usecs() in kernel/tsacct.c

    Hi,

    On Monday 25. February 2008, Jonathan Lim wrote:

    > +u64 jiffies_64_to_usecs(const u64 j)
    > +{
    > + return div64_64(j*HZ_TO_USEC_NUM + HZ_TO_USEC_DEN-1, HZ_TO_USEC_DEN);
    > +}
    > +EXPORT_SYMBOL(jiffies_64_to_usecs);


    Please also adapt the "BITS_PER_LONG == 32" part from jiffies_to_usecs(), it
    should provide enough resolution to avoid the div64_64() here.

    bye, Roman
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