All of lore.kernel.org
 help / color / mirror / Atom feed
From: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
To: linux-ia64@vger.kernel.org
Subject: Re: [PATCH 3/9] ia64: VIRT_CPU_ACCOUNTING (accurate cpu time accounting)
Date: Tue, 30 Oct 2007 02:25:55 +0000	[thread overview]
Message-ID: <47269633.8050409@jp.fujitsu.com> (raw)
In-Reply-To: <4714BE38.60807@jp.fujitsu.com>

Simon Horman wrote:
> On Tue, Oct 16, 2007 at 10:35:52PM +0900, Hidetoshi Seto wrote:
>> +#define cputime_to_jiffies(__ct)	((__ct) * HZ / NSEC_PER_SEC)
>> +#define jiffies_to_cputime(__jif)	((__jif) * NSEC_PER_SEC / HZ)
>> +#define cputime64_to_jiffies64(__ct)	((__ct) * HZ / NSEC_PER_SEC)
>> +#define jiffies64_to_cputime64(__jif)	((__jif) * NSEC_PER_SEC / HZ)
> 
> It looks like cputime64_to_jiffies64 and cputime_to_jiffies will
> overflow at (((2^64 -1) / HZ) + 1) ns. In the case where HZ is 1000,
> this means it will overflow at (584/1000) years or about 213 days.
> Similarly for cputime_to_clock_t(). Is this a problem?

Exactly.
I guess NSEC_PER_SEC is permanently 10^9, and larger HZ will not be
required soon in this century. Does the following help us?

#define cputime64_to_jiffies64(__ct)	((__ct) / (NSEC_PER_SEC / HZ))
#define jiffies64_to_cputime64(__jif)	((__jif) * (NSEC_PER_SEC / HZ))

Thanks,
H.Seto

  parent reply	other threads:[~2007-10-30  2:25 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-10-16 13:35 [PATCH 3/9] ia64: VIRT_CPU_ACCOUNTING (accurate cpu time accounting) Hidetoshi Seto
2007-10-30  1:40 ` Simon Horman
2007-10-30  2:25 ` Hidetoshi Seto [this message]
2007-10-30  2:41 ` Simon Horman

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=47269633.8050409@jp.fujitsu.com \
    --to=seto.hidetoshi@jp.fujitsu.com \
    --cc=linux-ia64@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.