| Message ID | 1448288921-30307-9-git-send-email-juri.lelli@arm.com (mailing list archive) |
|---|---|
| State | RFC, archived |
| Headers | show |
On 23/11/15 14:28, Juri Lelli wrote: > Add a sysfs cpu_capacity attribute with which it is possible to read and > write (thus over-writing default values) CPUs capacity. This might be > useful in situation where there is no way to get proper default values > at boot time. > > The new attribute shows up as: > > /sys/devices/system/cpu/cpu*/cpu_capacity > This sysfs interface is not really needed for arm or arm64. People can build the dt blob if they want to change the values. Less code to carry ... Let's focus on the core functionality, which is parsing cpu capacity from dt file to task scheduler for heterogeneous systems. [...] -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, Dec 10, 2015 at 02:15:04PM +0000, Dietmar Eggemann wrote: > On 23/11/15 14:28, Juri Lelli wrote: > > The new attribute shows up as: > > /sys/devices/system/cpu/cpu*/cpu_capacity > This sysfs interface is not really needed for arm or arm64. People can > build the dt blob if they want to change the values. Less code to carry > ... Let's focus on the core functionality, which is parsing cpu capacity > from dt file to task scheduler for heterogeneous systems. That does make the tuning process much more cumbersome - users have to rebuild and reboot to tweak the numbers rather than just tweaking the numbers and rerunning the benchmark (which seems like something people would want to automate).
Hi, On 10/12/15 15:59, Mark Brown wrote: > On Thu, Dec 10, 2015 at 02:15:04PM +0000, Dietmar Eggemann wrote: > > On 23/11/15 14:28, Juri Lelli wrote: > > > > The new attribute shows up as: > > > > /sys/devices/system/cpu/cpu*/cpu_capacity > > > This sysfs interface is not really needed for arm or arm64. People can > > build the dt blob if they want to change the values. Less code to carry > > ... Let's focus on the core functionality, which is parsing cpu capacity > > from dt file to task scheduler for heterogeneous systems. > > That does make the tuning process much more cumbersome - users have to > rebuild and reboot to tweak the numbers rather than just tweaking the > numbers and rerunning the benchmark (which seems like something people > would want to automate). IMHO, this is not a tuning interface. It is an alternative interface, w.r.t. DTs, that we could use to provide default capacity values to the kernel. I'm proposing both here as they make both sense to me. Then we might dedice for which one to go (or if we need some other way) or to keep both for flexibility. Best, - Juri -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, Dec 10, 2015 at 06:01:59PM +0000, Juri Lelli wrote: > On 10/12/15 15:59, Mark Brown wrote: > > On Thu, Dec 10, 2015 at 02:15:04PM +0000, Dietmar Eggemann wrote: > > > On 23/11/15 14:28, Juri Lelli wrote: > > > > The new attribute shows up as: > > > > /sys/devices/system/cpu/cpu*/cpu_capacity > > > This sysfs interface is not really needed for arm or arm64. People can > > > build the dt blob if they want to change the values. Less code to carry > > > ... Let's focus on the core functionality, which is parsing cpu capacity > > > from dt file to task scheduler for heterogeneous systems. > > That does make the tuning process much more cumbersome - users have to > > rebuild and reboot to tweak the numbers rather than just tweaking the > > numbers and rerunning the benchmark (which seems like something people > > would want to automate). > IMHO, this is not a tuning interface. It is an alternative interface, > w.r.t. DTs, that we could use to provide default capacity values to the > kernel. I'm proposing both here as they make both sense to me. Then we > might dedice for which one to go (or if we need some other way) or to > keep both for flexibility. Kind of repeating what I said in the other mail but I'd say that any interface which provides a mechanism for setting a magic number that influences system performance is providing tuning. It's hard to see how else to describe it to be honest.
diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c index 4423cc5..5c9e477 100644 --- a/arch/arm64/kernel/topology.c +++ b/arch/arm64/kernel/topology.c @@ -35,6 +35,74 @@ static void set_capacity_scale(unsigned int cpu, unsigned long capacity) per_cpu(cpu_scale, cpu) = capacity; } +#ifdef CONFIG_PROC_SYSCTL +#include <asm/cpu.h> +#include <linux/string.h> +static ssize_t show_cpu_capacity(struct device *dev, + struct device_attribute *attr, + char *buf) +{ + struct cpu *cpu = container_of(dev, struct cpu, dev); + ssize_t rc; + int cpunum = cpu->dev.id; + unsigned long capacity = arch_scale_cpu_capacity(NULL, cpunum); + + rc = sprintf(buf, "%lu\n", capacity); + + return rc; +} + +static ssize_t store_cpu_capacity(struct device *dev, + struct device_attribute *attr, + const char *buf, + size_t count) +{ + struct cpu *cpu = container_of(dev, struct cpu, dev); + int this_cpu = cpu->dev.id, i; + unsigned long new_capacity; + ssize_t ret; + + if (count) { + char *p = (char *) buf; + + ret = kstrtoul(p, 0, &new_capacity); + if (ret) + return ret; + if (new_capacity > SCHED_CAPACITY_SCALE) + return -EINVAL; + + for_each_cpu(i, &cpu_topology[this_cpu].core_sibling) + set_capacity_scale(i, new_capacity); + } + + return count; +} + +static DEVICE_ATTR(cpu_capacity, + 0644, + show_cpu_capacity, + store_cpu_capacity); + +static int register_cpu_capacity_sysctl(void) +{ + int i; + struct device *cpu; + + for_each_possible_cpu(i) { + cpu = get_cpu_device(i); + if (!cpu) { + pr_err("%s: too early to get CPU%d device!\n", + __func__, i); + continue; + } + device_create_file(cpu, &dev_attr_cpu_capacity); + } + + return 0; +} +late_initcall(register_cpu_capacity_sysctl); +#endif + static u32 capacity_scale = SCHED_CAPACITY_SCALE; static void __init parse_cpu_capacity(struct device_node *cpu_node, int cpu)
Add a sysfs cpu_capacity attribute with which it is possible to read and write (thus over-writing default values) CPUs capacity. This might be useful in situation where there is no way to get proper default values at boot time. The new attribute shows up as: /sys/devices/system/cpu/cpu*/cpu_capacity Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Mark Brown <broonie@linaro.org> Cc: Sudeep Holla <sudeep.holla@arm.com> Signed-off-by: Juri Lelli <juri.lelli@arm.com> --- arch/arm64/kernel/topology.c | 68 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 68 insertions(+)