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8d38805d3d
Currently the task scheduler suffers from an O(n) lookup when
skipping tasks that are not for the current thread. The reason
is that eb32_lookup_ge() has no information about the current
thread so it always revisits many tasks for other threads before
finding its own tasks.
This is particularly visible with HTTP/2 since the number of
concurrent streams created at once causes long series of tasks
for the same stream in the scheduler. With only 10 connections
and 100 streams each, by running on two threads, the performance
drops from 640kreq/s to 11.2kreq/s! Lookup metrics show that for
only 200000 task lookups, 430 million skips had to be performed,
which means that on average, each lookup leads to 2150 nodes to
be visited.
This commit backports the principle of scope lookups for ebtrees
from the ebtree_v7 development tree. The idea is that each node
contains a mask indicating the union of the scopes for the nodes
below it, which is fed during insertion, and used during lookups.
Then during lookups, branches that do not contain any leaf matching
the requested scope are simply ignored. This perfectly matches a
thread mask, allowing a thread to only extract the tasks it cares
about from the run queue, and to always find them in O(log(n))
instead of O(n). Thus the scheduler uses tid_bit and
task->thread_mask as the ebtree scope here.
Doing this has recovered most of the performance, as can be seen on
the test below with two threads, 10 connections, 100 streams each,
and 1 million requests total :
Before After Gain
test duration : 89.6s 4.73s x19
HTTP requests/s (DEBUG) : 11200 211300 x19
HTTP requests/s (PROD) : 15900 447000 x28
spin_lock time : 85.2s 0.46s /185
time per lookup : 13us 40ns /325
Even when going to 6 threads (on 3 hyperthreaded CPU cores), the
performance stays around 284000 req/s, showing that the contention
is much lower.
A test showed that there's no benefit in using this for the wait queue
though.
93 lines
3.7 KiB
C
93 lines
3.7 KiB
C
/*
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* include/types/task.h
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* Macros, variables and structures for task management.
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*
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* Copyright (C) 2000-2010 Willy Tarreau - w@1wt.eu
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation, version 2.1
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* exclusively.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef _TYPES_TASK_H
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#define _TYPES_TASK_H
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#include <sys/time.h>
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#include <common/config.h>
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#include <common/mini-clist.h>
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#include <eb32sctree.h>
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#include <eb32tree.h>
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/* values for task->state */
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#define TASK_SLEEPING 0x00 /* task sleeping */
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#define TASK_RUNNING 0x01 /* the task is currently running */
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#define TASK_WOKEN_INIT 0x02 /* woken up for initialisation purposes */
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#define TASK_WOKEN_TIMER 0x04 /* woken up because of expired timer */
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#define TASK_WOKEN_IO 0x08 /* woken up because of completed I/O */
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#define TASK_WOKEN_SIGNAL 0x10 /* woken up by a system signal */
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#define TASK_WOKEN_MSG 0x20 /* woken up by another task's message */
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#define TASK_WOKEN_RES 0x40 /* woken up because of available resource */
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#define TASK_WOKEN_OTHER 0x80 /* woken up for an unspecified reason */
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/* use this to check a task state or to clean it up before queueing */
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#define TASK_WOKEN_ANY (TASK_WOKEN_OTHER|TASK_WOKEN_INIT|TASK_WOKEN_TIMER| \
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TASK_WOKEN_IO|TASK_WOKEN_SIGNAL|TASK_WOKEN_MSG| \
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TASK_WOKEN_RES)
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/* Additional wakeup info may be passed in the state by lef-shifting the value
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* by this number of bits. Not more than 8 bits are guaranteed to be delivered.
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* System signals may use that too.
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*/
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#define TASK_REASON_SHIFT 8
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struct notification {
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struct list purge_me; /* Part of the list of signals to be purged in the
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case of the LUA execution stack crash. */
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struct list wake_me; /* Part of list of signals to be targeted if an
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event occurs. */
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struct task *task; /* The task to be wake if an event occurs. */
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#ifdef USE_THREAD
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HA_SPINLOCK_T lock;
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#endif
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};
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/* The base for all tasks */
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struct task {
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struct eb32sc_node rq; /* ebtree node used to hold the task in the run queue */
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unsigned short state; /* task state : bit field of TASK_* */
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unsigned short pending_state; /* pending states for running talk */
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short nice; /* the task's current nice value from -1024 to +1024 */
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unsigned int calls; /* number of times ->process() was called */
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struct task * (*process)(struct task *t); /* the function which processes the task */
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void *context; /* the task's context */
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struct eb32_node wq; /* ebtree node used to hold the task in the wait queue */
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int expire; /* next expiration date for this task, in ticks */
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unsigned long thread_mask; /* mask of thread IDs authorized to process the task */
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};
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/*
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* The task callback (->process) is responsible for updating ->expire. It must
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* return a pointer to the task itself, except if the task has been deleted, in
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* which case it returns NULL so that the scheduler knows it must not check the
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* expire timer. The scheduler will requeue the task at the proper location.
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*/
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#endif /* _TYPES_TASK_H */
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/*
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* Local variables:
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* c-indent-level: 8
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* c-basic-offset: 8
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* End:
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*/
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