On 4/14/21 4:30 PM, Steven Rostedt wrote:
> On Thu, 8 Apr 2021 16:13:20 +0200
> Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> wrote:
>
>> +/**
>> + * hwlat_mode_write - Write function for "mode" entry
>> + * @filp: The active open file structure
>> + * @ubuf: The user buffer that contains the value to write
>> + * @cnt: The maximum number of bytes to write to "file"
>> + * @ppos: The current position in @file
>> + *
>> + * This function provides a write implementation for the "mode" interface
>> + * to the hardware latency detector. hwlatd has different operation modes.
>> + * The "none" sets the allowed cpumask for a single hwlatd thread at the
>> + * startup and lets the scheduler handle the migration. The default mode is
>> + * the "round-robin" one, in which a single hwlatd thread runs, migrating
>> + * among the allowed CPUs in a round-robin fashion.
>> + */
>> +static ssize_t hwlat_mode_write(struct file *filp, const char __user *ubuf,
>> + size_t cnt, loff_t *ppos)
>> +{
>> + const char *mode;
>> + char buf[64];
>> + int ret;
>> + int i;
>> +
>> + if (hwlat_busy)
>> + return -EBUSY;
>
> So we can't switch modes while running?
>
As you mentioned in the patch 3/5, this limitation was added because
of the running threads. But, yes, stopping and starting the tracer to
re-create the threads should work as well. I will try it for the next round.
> Also, with this implemented, you can remove the disable_migrate variable,
> and just switch the mode to NONE when it's detected that the affinity mask
> of the thread has been changed.
>
That was my initial intention with the NONE mode, but I feared breaking
something by removing the "migrate_disable" logic. If you do not think it is
a problem, I will remove the migrate disable and just change the mode.
-- Daniel
> -- Steve
>
>
>> +
>> + if (cnt >= sizeof(buf))
>> + return -EINVAL;
>> +
>> + if (copy_from_user(buf, ubuf, cnt))
>> + return -EFAULT;
>> +
>> + buf[cnt] = 0;
>> +
>> + mode = strstrip(buf);
>> +
>> + ret = -EINVAL;
>> +
>> + for (i = 0; i < MODE_MAX; i++) {
>> + if (strcmp(mode, thread_mode_str[i]) == 0) {
>> + hwlat_data.thread_mode = i;
>> + ret = cnt;
>> + }
>> + }
>> +
>> + *ppos += cnt;
>> +
>> + return cnt;
>> +}
>> +
>> +
>
