|From:||Krishna Kumar <email@example.com>|
|Subject:||[PATCH 0/2] workqueue: Two API's to update delayed works quickly|
|Date:||Mon, 22 Sep 2008 09:34:04 +0530|
|Cc:||firstname.lastname@example.org, Krishna Kumar <email@example.com>|
From: Krishna Kumar <firstname.lastname@example.org> Implement two API's for quickly updating delayed works: void schedule_update_delayed_work(struct delayed_work *dwork, unsigned long delay); void queue_update_delayed_work(struct workqueue_struct *wq, struct delayed_work *dwork, unsigned long delay); These API's are useful to update an existing work entry more efficiently (but can be used to queue a new work entry too) when the operation is done very frequently. The rationale is to save time of first cancelling work/timer and adding work/timer when the same work is added many times in quick succession. An additional optimization is to do nothing when events are queued within 1 jiffy past the expiry time. However this can result in the work being queue'd upto 1 jiffy before the minimum time requested (but if another request comes 1 jiffy or more later, the work expires at the correct time). The assumption behind this optimization is that the work scheduled doesn't require 100% accuracy at the expense of performance. But if that is a faulty assumption, the 'time_in_range()' call can be changed to 'jiffies + delay == timer->expires'. queue_update_delayed_work_on() and schedule_update_delayed_work_on() are not implemented as there are no users which can take advantage of these variations. Example possible users (FS's, wireless drivers): ------------------------------------------------ lbs_scan_networks, nfs4_renew_state, ocfs2_schedule_truncate_log_flush, nfs4_schedule_state_renewal, afs_flush_callback_breaks, afs_reap_server, afs_purge_servers, afs_vlocation_reaper, afs_vlocation_purge, o2hb_arm_write_timeout, lbs_scan_networks, isr_indicate_rf_kill, lbs_postpone_association_work, isr_scan_complete, ipw_radio_kill_sw, __ipw_led_activity_on, ipw_radio_kill_sw, ds2760_battery_resume, etc. Performance (numbers in jiffies): --------------------------------- These API's are useful in following cases: a. add followed by cancel+add with long period between the add's. Time saved is the time to clear and re-setting the WORK_STRUCT_PENDING bit, plus the reduction of one API call. b. add followed by cancel+add with very short time between the add's. Time saved is all of above, plus avoid cancelling and re-adding. The results below are testing this case (with HZ = 1000). 1. queue_delayed_work+cancel vs queue_update_delayed_work on 1 cpu. Queue the same entry on same cpu serially - do this many times. Laptop (Xeon 2 cpu): Saves 83.7% ORG: Time: 41654 NEW: Time: 6804 Server (x86-64, 4 cpu): Saves 93.8% ORG: Time: 211488 NEW: Time: 13187 2. queue_delayed_work+cancel vs queue_update_delayed_work on 'N' cpus in parallel. Queue 'N' different entries on 'N' cpu's in paralle - do this many times. Laptop (Xeon 2 cpu): Saves 95.7% ORG: Time: 146064, 182160 NEW: Time: 7014, 7045 Server (x86-64, 4 cpu): Saves 93.7% ORG: Time: 165255, 225159, 227658, 237000 NEW: Time: 13446, 13449, 13455, 13477 3. schedule_delayed_work+cancel vs schedule_update_delayed_work on 1 cpu. Queue the same entry on same cpu serially - do this many times. Laptop (Xeon 2 cpu): Saves 83.3% ORG: Time: 41878 NEW: Time: 6987 Server (x86-64, 4 cpu): Saves 92.3% ORG: Time: 184893 NEW: Time: 14205 4. schedule_delayed_work+cancel vs schedule_update_delayed_work on 'N' cpus in parallel. Queue 'N' different entries on 'N' cpu's in parallel - do this many times. Laptop (Xeon 2 cpu): Saves 95.73% ORG: Time: 145147, 180987 NEW: Time: 6955, 6958 Server (x86-64, 4 cpu): Saves 94.5% ORG: Time: 165031, 263509, 277071, 321099 NEW: Time: 14211, 14211, 14216, 14242 [PATCH 1/2]: Implement the kernel API's [PATCH 2/2]: Modify some drivers to use the new APIs instead of the old ones Signed-off-by: Krishna Kumar <email@example.com> ---
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