RE: [PATCH 2/2] cpufreq: Fix ondemand to not request targets outside policy limits

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Booting with debug turned on on an Intel Nehalem server, notice the
following output in "dmesg":

...
cpufreq-core: target for CPU 0: 0 kHz, relation 0
acpi-cpufreq: acpi_cpufreq_target 0 (0)
freq-table: request for target 0 kHz (relation: 0) for cpu 0
freq-table: target is 9 (1596000 kHz, 9)
cpufreq-core: notification 0 of frequency transition to 1596000 kHz
cpufreq-core: notification 1 of frequency transition to 1596000 kHz
...

There are instances where "ondemand" asks for a target frequency of even 0.
More generally, "ondemand" can ask for freq_next < policy->min, whenever
"load" on the CPU drops to a level that satisfies the equation below:

	load < ((threshold - differential) * policy->min / policy->cur)

Hence, the patch below.

NOTE:
Drivers such as "acpi-cpufreq" can make use of the freq-table helper
function, cpufreq_frequency_table_target(), which presumably can take
a target frequency < policy->min, and still provide an "index" that
corresponds to Pn (lowest supported frequency). This can be seen in the
"dmesg" output above.

- naga -
 

>-----Original Message-----
>From: Thomas Renninger [mailto:trenn@xxxxxxx] 
>Sent: Monday, December 21, 2009 4:41 PM
>To: Chumbalkar, Nagananda
>Cc: davej@xxxxxxxxxx; mjg@xxxxxxxxxx; cpufreq@xxxxxxxxxxxxxxx; 
>linux-acpi@xxxxxxxxxxxxxxx; linux@xxxxxxxx
>Subject: [PATCH 2/2] cpufreq: Fix ondemand to not request 
>targets outside policy limits
>
>From: Nagananda.Chumbalkar@xxxxxx
>
>Dominik said:
>target_freq cannot be below policy->min or above policy->max. 
>If it were, the whole cpufreq subsystem is broken.
>
>But (answer):
>I think the "ondemand" governor can ask for a target frequency that is
>below policy->min.
>...
>A patch such as below may be needed to sanitize the target frequency 
>requested by "ondemand". The "conservative" governor already 
>has this check: 
>
>Signed-off-by: Thomas Renninger <trenn@xxxxxxx>
>
># diff -bur x/drivers/cpufreq/cpufreq_ondemand.c.orig 
>y/drivers/cpufreq/cpufreq_ondemand.c
>diff --git a/drivers/cpufreq/cpufreq_ondemand.c 
>b/drivers/cpufreq/cpufreq_ondemand.c
>index 4b34ade..bd444dc 100644
>--- a/drivers/cpufreq/cpufreq_ondemand.c
>+++ b/drivers/cpufreq/cpufreq_ondemand.c
>@@ -554,6 +554,9 @@ static void dbs_check_cpu(struct 
>cpu_dbs_info_s *this_dbs_info)
> 				(dbs_tuners_ins.up_threshold -
> 				 dbs_tuners_ins.down_differential);
> 
>+		if (freq_next < policy->min)
>+			freq_next = policy->min;
>+
> 		if (!dbs_tuners_ins.powersave_bias) {
> 			__cpufreq_driver_target(policy, freq_next,
> 					CPUFREQ_RELATION_L);
>--
To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[Index of Archives]     [Linux IBM ACPI]     [Linux Power Management]     [Linux Kernel]     [Linux Laptop]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Samba]     [Video 4 Linux]     [Device Mapper]     [Linux Resources]

  Powered by Linux