I have a machine where entering deep C-states broke. pm_qos was a hot candidate, but I couldn't find any way to double check without the need of recompiling.
While in this case it was a driver bug (ath9k): https://bugzilla.kernel.org/show_bug.cgi?id=27532 powertop or others may want to read out cpu_dma_latency restrictions which could be the cause of preventing a machine entering deeper C-states. Output with this patch: # default value of 2000 * USEC_PER_SEC (0x77359400) cat /dev/network_latency |hexdump 0000000 9400 7735 0000004 # value of 55 us which is the reason for not entering C2 cat /dev/cpu_dma_latency |hexdump 0000000 0037 0000 0000004 There is no reason to hide this info -> make pm_qos files readable. Signed-off-by: Thomas Renninger <[email protected]> CC: [email protected] CC: [email protected] --- kernel/pm_qos_params.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) Index: linux-2.6.37-master_build/kernel/pm_qos_params.c =================================================================== --- linux-2.6.37-master_build.orig/kernel/pm_qos_params.c +++ linux-2.6.37-master_build/kernel/pm_qos_params.c @@ -103,11 +103,14 @@ static struct pm_qos_object *pm_qos_arra static ssize_t pm_qos_power_write(struct file *filp, const char __user *buf, size_t count, loff_t *f_pos); +static ssize_t pm_qos_power_read(struct file *filp, char __user *buf, + size_t count, loff_t *f_pos); static int pm_qos_power_open(struct inode *inode, struct file *filp); static int pm_qos_power_release(struct inode *inode, struct file *filp); static const struct file_operations pm_qos_power_fops = { .write = pm_qos_power_write, + .read = pm_qos_power_read, .open = pm_qos_power_open, .release = pm_qos_power_release, .llseek = noop_llseek, @@ -376,6 +379,27 @@ static int pm_qos_power_release(struct i } +static ssize_t pm_qos_power_read(struct file *filp, char __user *buf, + size_t count, loff_t *f_pos) +{ + s32 value; + unsigned long flags; + struct pm_qos_object *o; + struct pm_qos_request_list *pm_qos_req = filp->private_data;; + + if (!pm_qos_req) + return -EINVAL; + if (!pm_qos_request_active(pm_qos_req)) + return -EINVAL; + + o = pm_qos_array[pm_qos_req->pm_qos_class]; + spin_lock_irqsave(&pm_qos_lock, flags); + value = pm_qos_get_value(o); + spin_unlock_irqrestore(&pm_qos_lock, flags); + + return simple_read_from_buffer(buf, count, f_pos, &value, sizeof(s32)); +} + static ssize_t pm_qos_power_write(struct file *filp, const char __user *buf, size_t count, loff_t *f_pos) { _______________________________________________ Power mailing list [email protected] http://www.bughost.org/mailman/listinfo/power
