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Message-ID: <b2082cef-2e23-253d-4833-542c3460972a@redhat.com>
Date: Tue, 16 May 2023 10:31:58 +0200
From: Hans de Goede <hdegoede@...hat.com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>,
Linux ACPI <linux-acpi@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Sakari Ailus <sakari.ailus@...ux.intel.com>
Subject: Re: [PATCH] ACPI: scan: Reduce overhead related to devices with
dependencies
Hi Rafael,
On 5/15/23 18:30, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> Notice that all of the objects for which the acpi_scan_check_dep()
> return value is greater than 0 are present in acpi_dep_list as consumers
> (there may be multiple entries for one object, but that is not a
> problem), so after carrying out the initial ACPI namespace walk in which
> devices with dependencies are skipped, acpi_bus_scan() can simply walk
> acpi_dep_list and enumerate all of the unique consumer objects from
> there and their descendants instead of walking the entire target branch
> of the ACPI namespace and looking for device objects that have not been
> enumerated yet in it.
>
> Because walking acpi_dep_list is generally less overhead than walking
> the entire ACPI namespace, use the observation above to reduce the
> system initialization overhead related to ACPI, which is particularly
> important on large systems.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> drivers/acpi/scan.c | 79 +++++++++++++++++++++++++++++++++++-------------
> include/acpi/acpi_bus.h | 2 +
> 2 files changed, 61 insertions(+), 20 deletions(-)
>
> Index: linux-pm/include/acpi/acpi_bus.h
> ===================================================================
> --- linux-pm.orig/include/acpi/acpi_bus.h
> +++ linux-pm/include/acpi/acpi_bus.h
> @@ -289,6 +289,8 @@ struct acpi_dep_data {
> acpi_handle supplier;
> acpi_handle consumer;
> bool honor_dep;
> + bool met;
> + bool free_when_met;
> };
>
> /* Performance Management */
> Index: linux-pm/drivers/acpi/scan.c
> ===================================================================
> --- linux-pm.orig/drivers/acpi/scan.c
> +++ linux-pm/drivers/acpi/scan.c
> @@ -2029,8 +2029,6 @@ static u32 acpi_scan_check_dep(acpi_hand
> return count;
> }
>
> -static bool acpi_bus_scan_second_pass;
> -
> static acpi_status acpi_bus_check_add(acpi_handle handle, bool check_dep,
> struct acpi_device **adev_p)
> {
> @@ -2050,10 +2048,8 @@ static acpi_status acpi_bus_check_add(ac
> return AE_OK;
>
> /* Bail out if there are dependencies. */
> - if (acpi_scan_check_dep(handle, check_dep) > 0) {
> - acpi_bus_scan_second_pass = true;
> + if (acpi_scan_check_dep(handle, check_dep) > 0)
> return AE_CTRL_DEPTH;
> - }
>
> fallthrough;
> case ACPI_TYPE_ANY: /* for ACPI_ROOT_OBJECT */
> @@ -2301,6 +2297,12 @@ static bool acpi_scan_clear_dep_queue(st
> return true;
> }
>
> +static void acpi_scan_delete_dep_data(struct acpi_dep_data *dep)
> +{
> + list_del(&dep->node);
> + kfree(dep);
> +}
> +
> static int acpi_scan_clear_dep(struct acpi_dep_data *dep, void *data)
> {
> struct acpi_device *adev = acpi_get_acpi_dev(dep->consumer);
> @@ -2311,8 +2313,10 @@ static int acpi_scan_clear_dep(struct ac
> acpi_dev_put(adev);
> }
>
> - list_del(&dep->node);
> - kfree(dep);
> + if (dep->free_when_met)
> + acpi_scan_delete_dep_data(dep);
> + else
> + dep->met = true;
>
> return 0;
> }
> @@ -2406,6 +2410,53 @@ struct acpi_device *acpi_dev_get_next_co
> }
> EXPORT_SYMBOL_GPL(acpi_dev_get_next_consumer_dev);
>
> +static void acpi_scan_postponed_branch(acpi_handle handle)
> +{
> + struct acpi_device *adev = NULL;
> +
> + if (ACPI_FAILURE(acpi_bus_check_add(handle, false, &adev)))
> + return;
> +
> + acpi_walk_namespace(ACPI_TYPE_ANY, handle, ACPI_UINT32_MAX,
> + acpi_bus_check_add_2, NULL, NULL, (void **)&adev);
> + acpi_bus_attach(adev, NULL);
> +}
> +
> +static void acpi_scan_postponed(void)
> +{
> + struct acpi_dep_data *dep, *tmp;
> +
> + mutex_lock(&acpi_dep_list_lock);
> +
> + list_for_each_entry_safe(dep, tmp, &acpi_dep_list, node) {
> + acpi_handle handle = dep->consumer;
> +
> + /*
> + * Even though the lock is released here, tmp is guaranteed to
> + * be valid, because none of the list entries following dep is
> + * marked as "free when met" and so they cannot be deleted.
> + */
> + mutex_unlock(&acpi_dep_list_lock);
> +
> + /*
> + * In case there are multiple acpi_dep_list entries with the
> + * same consumer, skip the current entry if the consumer device
> + * object corresponding to it is present already.
> + */
> + if (!acpi_fetch_acpi_dev(handle))
> + acpi_scan_postponed_branch(handle);
acpi_fetch_acpi_dev(handle) does not need/take the acpi_dep_list_lock,
so you can avoid a needless unlock/lock in case acpi_fetch_acpi_dev(handle)
finds a device already, which will happen quite regular since devices
with _DEP lists regularly have more then 1 dep so they will be present
as consumer on the _DEP list more then once.
So maybe:
list_for_each_entry_safe(dep, tmp, &acpi_dep_list, node) {
acpi_handle handle = dep->consumer;
struct acpi_device *device = acpi_fetch_acpi_dev(handle);
/*
* In case there are multiple acpi_dep_list entries with the
* same consumer, skip scanning the current entry if the consumer
* device object corresponding to it is present already.
*/
if (device)
goto check_dep;
/*
* Even though the lock is released here, tmp is guaranteed to
* be valid, because none of the list entries following dep is
* marked as "free when met" and so they cannot be deleted.
*/
mutex_unlock(&acpi_dep_list_lock);
acpi_scan_postponed_branch(handle);
mutex_lock(&acpi_dep_list_lock);
check_dep:
if (dep->met)
acpi_scan_delete_dep_data(dep);
else
dep->free_when_met = true;
}
?
Regards,
Hans
> +
> + mutex_unlock(&acpi_dep_list_lock);
> +}
> +
> /**
> * acpi_bus_scan - Add ACPI device node objects in a given namespace scope.
> * @handle: Root of the namespace scope to scan.
> @@ -2424,8 +2475,6 @@ int acpi_bus_scan(acpi_handle handle)
> {
> struct acpi_device *device = NULL;
>
> - acpi_bus_scan_second_pass = false;
> -
> /* Pass 1: Avoid enumerating devices with missing dependencies. */
>
> if (ACPI_SUCCESS(acpi_bus_check_add(handle, true, &device)))
> @@ -2438,19 +2487,9 @@ int acpi_bus_scan(acpi_handle handle)
>
> acpi_bus_attach(device, (void *)true);
>
> - if (!acpi_bus_scan_second_pass)
> - return 0;
> -
> /* Pass 2: Enumerate all of the remaining devices. */
>
> - device = NULL;
> -
> - if (ACPI_SUCCESS(acpi_bus_check_add(handle, false, &device)))
> - acpi_walk_namespace(ACPI_TYPE_ANY, handle, ACPI_UINT32_MAX,
> - acpi_bus_check_add_2, NULL, NULL,
> - (void **)&device);
> -
> - acpi_bus_attach(device, NULL);
> + acpi_scan_postponed();
>
> return 0;
> }
>
>
>
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