On Mon, 2012-11-19 at 09:10 +0100, Rafael J. Wysocki wrote: > On Tuesday, November 06, 2012 08:02:06 AM Toshi Kani wrote: > > This patch introduces acpi_pr_<level>(), where <level> is a kernel > > message level such as err/warn/info, to support improved logging > > messages for ACPI, esp. for hotplug operations. acpi_pr_<level>() > > appends "ACPI" prefix and ACPI object path to the messages. This > > improves diagnosis of hotplug operations since an error message in > > a log file identifies an object that caused an issue. > > > > acpi_pr_<level>() takes acpi_handle as an argument, which is passed > > to ACPI hotplug notify handlers from the ACPICA. Therefore, it is > > always available unlike other kernel objects, such as device. > > > > For example: > > acpi_pr_err(handle, "Device don't exist, dropping EJECT\n"); > > logs an error message like this at KERN_ERR. > > ACPI: \_SB_.SCK4.CPU4: Device don't exist, dropping EJECT > > > > ACPI drivers can use acpi_pr_<level>() when they need to identify > > a target ACPI object path in their messages, such as error cases. > > The usage model is similar to dev_<level>(). acpi_pr_<level>() can > > be used when device is not created/valid, which may be the case in > > ACPI hotplug handlers. ACPI object path is also consistent on the > > platform, unlike device name that changes over hotplug operations. > > > > ACPI drivers should use dev_<level>() when device is valid and > > acpi_pr_<level>() is already used by the caller in its error path. > > Device name provides more user friendly information. > > > > ACPI drivers also continue to use pr_<level>() when messages do not > > need to specify device information, such as boot-up messages. > > > > Note: ACPI_[WARNING|INFO|ERROR]() are intended for the ACPICA and > > are not associated with the kernel message level. > > Well, the idea is generally good, but unfortunately acpi_get_name() is > not a cheap operation. Namely, it takes the global namespace mutex, > so your acpi_printk() may be a source of serious contention on that > lock if used excessively from concurrent threads. > > Do you think you can address this problem? Hi Rafael, I agree with you that the interface name may sound too generic as if it can be used for any way. How about changing the interface name to acpi_hp_<level>() to clarify that it is intended for hot-plug operations only? The key goal is to be able to identify a failed device in hot-plug error messages, so that we can diagnose an issue. When used in hot-plug operations, especially in error paths, the lock contention is not an issue. In regular code path (i.e. non-hot-plug operations), dev_<level>() should be used since device object is available. Here is a measurement result for the interface. When there is no locking contention, acpi_get_name() is reasonably fast as it does not execute AML. Avg. acpi_get_name() 587 ns Avg. printk() 3420 ns Avg. kfree() 238 ns Avg. acpi_get_time()+kfree() 825 ns > Moreover, this also means that acpi_printk() cannot be used from interrupt > context, so it is not a printk() replacement, which at least should be > documented. Right. I will document it in the comment and change log. Thanks, -Toshi -- 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
