)]}' { "commit": "64c7c8f88559624abdbe12b5da6502e8879f8d28", "tree": "02f85a35ddd0f24dec70e5d6ecd61073578fd8d6", "parents": [ "5bfb5d690f36d316a5f3b4f7775fda996faa6b12" ], "author": { "name": "Nick Piggin", "email": "nickpiggin@yahoo.com.au", "time": "Tue Nov 08 21:39:04 2005 -0800" }, "committer": { "name": "Linus Torvalds", "email": "torvalds@g5.osdl.org", "time": "Wed Nov 09 07:56:33 2005 -0800" }, "message": "[PATCH] sched: resched and cpu_idle rework\n\nMake some changes to the NEED_RESCHED and POLLING_NRFLAG to reduce\nconfusion, and make their semantics rigid. Improves efficiency of\nresched_task and some cpu_idle routines.\n\n* In resched_task:\n- TIF_NEED_RESCHED is only cleared with the task\u0027s runqueue lock held,\n and as we hold it during resched_task, then there is no need for an\n atomic test and set there. The only other time this should be set is\n when the task\u0027s quantum expires, in the timer interrupt - this is\n protected against because the rq lock is irq-safe.\n\n- If TIF_NEED_RESCHED is set, then we don\u0027t need to do anything. It\n won\u0027t get unset until the task get\u0027s schedule()d off.\n\n- If we are running on the same CPU as the task we resched, then set\n TIF_NEED_RESCHED and no further action is required.\n\n- If we are running on another CPU, and TIF_POLLING_NRFLAG is *not* set\n after TIF_NEED_RESCHED has been set, then we need to send an IPI.\n\nUsing these rules, we are able to remove the test and set operation in\nresched_task, and make clear the previously vague semantics of\nPOLLING_NRFLAG.\n\n* In idle routines:\n- Enter cpu_idle with preempt disabled. When the need_resched() condition\n becomes true, explicitly call schedule(). This makes things a bit clearer\n (IMO), but haven\u0027t updated all architectures yet.\n\n- Many do a test and clear of TIF_NEED_RESCHED for some reason. According\n to the resched_task rules, this isn\u0027t needed (and actually breaks the\n assumption that TIF_NEED_RESCHED is only cleared with the runqueue lock\n held). So remove that. Generally one less locked memory op when switching\n to the idle thread.\n\n- Many idle routines clear TIF_POLLING_NRFLAG, and only set it in the inner\n most polling idle loops. The above resched_task semantics allow it to be\n set until before the last time need_resched() is checked before going into\n a halt requiring interrupt wakeup.\n\n Many idle routines simply never enter such a halt, and so POLLING_NRFLAG\n can be always left set, completely eliminating resched IPIs when rescheduling\n the idle task.\n\n POLLING_NRFLAG width can be increased, to reduce the chance of resched IPIs.\n\nSigned-off-by: Nick Piggin \u003cnpiggin@suse.de\u003e\nCc: Ingo Molnar \u003cmingo@elte.hu\u003e\nCc: Con Kolivas \u003ckernel@kolivas.org\u003e\nSigned-off-by: Andrew Morton \u003cakpm@osdl.org\u003e\nSigned-off-by: Linus Torvalds \u003ctorvalds@osdl.org\u003e\n", "tree_diff": [ { "type": "add", "old_id": "0000000000000000000000000000000000000000", "old_mode": 0, "old_path": "/dev/null", "new_id": "941615a9769b91ea0cee31723023c600645db67d", "new_mode": 33188, "new_path": "Documentation/sched-arch.txt" }, { "type": "modify", "old_id": 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