From: Thomas Gleixner <tglx@linutronix.de>
To: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc: Kate Stewart <kstewart@linuxfoundation.org>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
x86@kernel.org, Ashok Raj <ashok.raj@intel.com>,
Arnd Bergmann <arnd@arndb.de>,
Peter Zijlstra <peterz@infradead.org>,
Philippe Ombredanne <pombredanne@nexb.com>,
Randy Dunlap <rdunlap@infradead.org>,
Clemens Ladisch <clemens@ladisch.de>,
linux-kernel@vger.kernel.org,
Stephane Eranian <eranian@google.com>,
Ricardo Neri <ricardo.neri@intel.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
iommu@lists.linux-foundation.org, Tony Luck <tony.luck@intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Andi Kleen <andi.kleen@intel.com>, Borislav Petkov <bp@suse.de>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: [RFC PATCH v4 03/21] x86/hpet: Calculate ticks-per-second in a separate function
Date: Fri, 14 Jun 2019 17:59:34 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.21.1906141756430.1722@nanos.tec.linutronix.de> (raw)
In-Reply-To: <alpine.DEB.2.21.1906141749330.1722@nanos.tec.linutronix.de>
On Fri, 14 Jun 2019, Thomas Gleixner wrote:
> On Thu, 23 May 2019, Ricardo Neri wrote:
> > int hpet_alloc(struct hpet_data *hdp)
> > {
> > u64 cap, mcfg;
> > @@ -844,7 +867,6 @@ int hpet_alloc(struct hpet_data *hdp)
> > struct hpets *hpetp;
> > struct hpet __iomem *hpet;
> > static struct hpets *last;
> > - unsigned long period;
> > unsigned long long temp;
> > u32 remainder;
> >
> > @@ -894,12 +916,7 @@ int hpet_alloc(struct hpet_data *hdp)
> >
> > last = hpetp;
> >
> > - period = (cap & HPET_COUNTER_CLK_PERIOD_MASK) >>
> > - HPET_COUNTER_CLK_PERIOD_SHIFT; /* fs, 10^-15 */
> > - temp = 1000000000000000uLL; /* 10^15 femtoseconds per second */
> > - temp += period >> 1; /* round */
> > - do_div(temp, period);
> > - hpetp->hp_tick_freq = temp; /* ticks per second */
> > + hpetp->hp_tick_freq = hpet_get_ticks_per_sec(cap);
>
> Why are we actually computing this over and over?
>
> In hpet_enable() which is the first function invoked we have:
>
> /*
> * The period is a femto seconds value. Convert it to a
> * frequency.
> */
> freq = FSEC_PER_SEC;
> do_div(freq, hpet_period);
> hpet_freq = freq;
>
> So we already have ticks per second, aka frequency, right? So why do we
> need yet another function instead of using the value which is computed
> once? The frequency of the HPET channels has to be identical no matter
> what. If it's not HPET is broken beyond repair.
Aside of that this change breaks the IA64 support for /dev/hpet.
Thanks,
tglx
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
next prev parent reply other threads:[~2019-06-14 15:59 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-24 1:16 [RFC PATCH v4 00/21] Implement an HPET-based hardlockup detector Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 01/21] x86/msi: Add definition for NMI delivery mode Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 02/21] x86/hpet: Expose hpet_writel() in header Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 03/21] x86/hpet: Calculate ticks-per-second in a separate function Ricardo Neri
2019-06-14 15:54 ` Thomas Gleixner
2019-06-14 15:59 ` Thomas Gleixner [this message]
2019-06-18 22:48 ` Ricardo Neri
2019-06-18 23:13 ` Thomas Gleixner
2019-05-24 1:16 ` [RFC PATCH v4 04/21] x86/hpet: Add hpet_set_comparator() for periodic and one-shot modes Ricardo Neri
2019-06-14 18:17 ` Thomas Gleixner
2019-06-18 22:48 ` Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 05/21] x86/hpet: Reserve timer for the HPET hardlockup detector Ricardo Neri
2019-06-11 19:54 ` Thomas Gleixner
2019-06-14 1:14 ` Ricardo Neri
2019-06-14 16:10 ` Thomas Gleixner
2019-06-18 22:48 ` Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 06/21] x86/hpet: Configure the timer used by the " Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 07/21] watchdog/hardlockup: Define a generic function to detect hardlockups Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 08/21] watchdog/hardlockup: Decouple the hardlockup detector from perf Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 09/21] x86/nmi: Add a NMI_WATCHDOG NMI handler category Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 10/21] watchdog/hardlockup: Add function to enable NMI watchdog on all allowed CPUs at once Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 11/21] x86/watchdog/hardlockup: Add an HPET-based hardlockup detector Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 12/21] watchdog/hardlockup/hpet: Adjust timer expiration on the number of monitored CPUs Ricardo Neri
2019-06-11 20:11 ` Thomas Gleixner
2019-06-18 22:46 ` Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 13/21] x86/watchdog/hardlockup/hpet: Determine if HPET timer caused NMI Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 14/21] watchdog/hardlockup: Use parse_option_str() to handle "nmi_watchdog" Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 15/21] watchdog/hardlockup/hpet: Only enable the HPET watchdog via a boot parameter Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 16/21] x86/watchdog: Add a shim hardlockup detector Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 17/21] x86/tsc: Switch to perf-based hardlockup detector if TSC become unstable Ricardo Neri
2019-06-07 0:35 ` Stephane Eranian via iommu
2019-06-07 14:14 ` Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 18/21] x86/apic: Add a parameter for the APIC delivery mode Ricardo Neri
2019-06-16 9:55 ` Thomas Gleixner
2019-06-18 22:47 ` Ricardo Neri
2019-06-18 23:15 ` Thomas Gleixner
2019-05-24 1:16 ` [RFC PATCH v4 19/21] iommu/vt-d: Rework prepare_irte() to support per-irq " Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 20/21] iommu/vt-d: hpet: Reserve an interrupt remampping table entry for watchdog Ricardo Neri
2019-06-16 18:42 ` Thomas Gleixner
2019-06-16 19:21 ` Thomas Gleixner
2019-06-17 8:25 ` Thomas Gleixner
2019-06-17 21:38 ` Stephane Eranian via iommu
2019-06-17 23:08 ` Thomas Gleixner
2019-06-19 15:43 ` Jacob Pan
2019-06-21 15:33 ` Thomas Gleixner
2019-06-21 17:31 ` Jacob Pan
2019-06-21 18:39 ` Jacob Pan
2019-06-21 20:05 ` Thomas Gleixner
2019-06-21 23:55 ` Ricardo Neri
2019-06-22 7:21 ` Thomas Gleixner
2019-10-18 2:48 ` Ricardo Neri
2019-06-18 22:45 ` Ricardo Neri
2019-05-24 1:16 ` [RFC PATCH v4 21/21] x86/watchdog/hardlockup/hpet: Support interrupt remapping Ricardo Neri
2019-06-16 8:44 ` Thomas Gleixner
2019-06-16 8:53 ` Thomas Gleixner
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=alpine.DEB.2.21.1906141756430.1722@nanos.tec.linutronix.de \
--to=tglx@linutronix.de \
--cc=andi.kleen@intel.com \
--cc=arnd@arndb.de \
--cc=ashok.raj@intel.com \
--cc=bp@suse.de \
--cc=clemens@ladisch.de \
--cc=eranian@google.com \
--cc=hpa@zytor.com \
--cc=iommu@lists.linux-foundation.org \
--cc=kstewart@linuxfoundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=pombredanne@nexb.com \
--cc=rafael.j.wysocki@intel.com \
--cc=ravi.v.shankar@intel.com \
--cc=rdunlap@infradead.org \
--cc=ricardo.neri-calderon@linux.intel.com \
--cc=ricardo.neri@intel.com \
--cc=tony.luck@intel.com \
--cc=x86@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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).