From: Jacob Pan <jacob.jun.pan@linux.intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
Borislav Petkov <bp@alien8.de>,
LKML <linux-kernel@vger.kernel.org>,
Linux PM <linux-pm@vger.kernel.org>,
Rafael Wysocki <rafael.j.wysocki@intel.com>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
X86 Kernel <x86@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
jacob.jun.pan@linux.intel.com
Subject: Re: [PATCH v2 2/2] powercap/rapl: reduce ipi calls
Date: Wed, 13 Jan 2016 14:11:15 -0800 [thread overview]
Message-ID: <20160113141115.59535b45@yairi> (raw)
In-Reply-To: <alpine.DEB.2.11.1601132257550.3575@nanos>
On Wed, 13 Jan 2016 23:02:33 +0100 (CET)
Thomas Gleixner <tglx@linutronix.de> wrote:
> On Wed, 13 Jan 2016, Srinivas Pandruvada wrote:
> > On Wed, 2016-01-13 at 22:26 +0100, Borislav Petkov wrote:
> > > rmwmsrl_safe_on_cpu(policy->cpu, MSR_IA32_PERF_CTL,
> > > INTEL_PERF_CTL_MASK,
> > > (u32)sfi_cpufreq_array[next_perf_state].ctr
> > > l_val & INTEL_PERF_CTL_MASK);
> > >
> > > Yikes!
> > >
> > > So yes, it can work but it is ugly, hard to parse and use, not
> > > generic
> > > enough, etc, etc.
> > >
> > > So thanks, but no thanks.
> > >
> > I agree, in some cases it will not make much sense to use read-
> > modify_write calls, the user may decide whether it makes sense or
> > not. But such interface is not new to Linux kernel:
> >
> > regmap_update_bits(), which is referenced for 346 times.
> >
> > Are you saying that any such calls are not useful?
>
> There are certainly cases when such calls are useful. And those cases
> are when we have a sufficiently big occurence of similar code which
> is sufficiently complex to justify the library code and the export.
>
The balance of pros and cons depends on the number of occurrence. The
lib call overhead is constant where saving from the callers are
multiplied. Anyway, I will go back to my original code until we have
enough callers to tip the balance.
next prev parent reply other threads:[~2016-01-13 22:11 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-13 1:11 [PATCH v2 0/2] Reduce IPI calls for remote msr access Jacob Pan
2016-01-13 1:11 ` [PATCH v2 1/2] x86/msr: add on cpu read/modify/write function Jacob Pan
2016-01-13 1:11 ` [PATCH v2 2/2] powercap/rapl: reduce ipi calls Jacob Pan
2016-01-13 9:47 ` Thomas Gleixner
2016-01-13 16:21 ` Jacob Pan
2016-01-13 16:36 ` Borislav Petkov
2016-01-13 17:51 ` Jacob Pan
2016-01-13 18:04 ` Borislav Petkov
2016-01-13 18:21 ` Jacob Pan
2016-01-13 19:16 ` Borislav Petkov
2016-01-13 20:10 ` Jacob Pan
2016-01-13 21:26 ` Borislav Petkov
2016-01-13 21:54 ` Srinivas Pandruvada
2016-01-13 22:02 ` Thomas Gleixner
2016-01-13 22:11 ` Jacob Pan [this message]
2016-01-13 22:23 ` H. Peter Anvin
2016-01-13 22:16 ` Borislav Petkov
2016-01-13 22:39 ` Srinivas Pandruvada
2016-01-13 22:20 ` Jacob Pan
2016-01-13 22:29 ` Borislav Petkov
2016-01-13 21:49 ` Thomas Gleixner
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