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Diffstat (limited to 'drivers/block/paride/Transition-notes')
| -rw-r--r-- | drivers/block/paride/Transition-notes | 128 |
1 files changed, 0 insertions, 128 deletions
diff --git a/drivers/block/paride/Transition-notes b/drivers/block/paride/Transition-notes deleted file mode 100644 index 70374907c020..000000000000 --- a/drivers/block/paride/Transition-notes +++ /dev/null @@ -1,128 +0,0 @@ -Lemma 1: - If ps_tq is scheduled, ps_tq_active is 1. ps_tq_int() can be called - only when ps_tq_active is 1. -Proof: All assignments to ps_tq_active and all scheduling of ps_tq happen - under ps_spinlock. There are three places where that can happen: - one in ps_set_intr() (A) and two in ps_tq_int() (B and C). - Consider the sequnce of these events. A can not be preceded by - anything except B, since it is under if (!ps_tq_active) under - ps_spinlock. C is always preceded by B, since we can't reach it - other than through B and we don't drop ps_spinlock between them. - IOW, the sequence is A?(BA|BC|B)*. OTOH, number of B can not exceed - the sum of numbers of A and C, since each call of ps_tq_int() is - the result of ps_tq execution. Therefore, the sequence starts with - A and each B is preceded by either A or C. Moments when we enter - ps_tq_int() are sandwiched between {A,C} and B in that sequence, - since at any time number of B can not exceed the number of these - moments which, in turn, can not exceed the number of A and C. - In other words, the sequence of events is (A or C set ps_tq_active to - 1 and schedule ps_tq, ps_tq is executed, ps_tq_int() is entered, - B resets ps_tq_active)*. - - -consider the following area: - * in do_pd_request1(): to calls of pi_do_claimed() and return in - case when pd_req is NULL. - * in next_request(): to call of do_pd_request1() - * in do_pd_read(): to call of ps_set_intr() - * in do_pd_read_start(): to calls of pi_do_claimed(), next_request() -and ps_set_intr() - * in do_pd_read_drq(): to calls of pi_do_claimed() and next_request() - * in do_pd_write(): to call of ps_set_intr() - * in do_pd_write_start(): to calls of pi_do_claimed(), next_request() -and ps_set_intr() - * in do_pd_write_done(): to calls of pi_do_claimed() and next_request() - * in ps_set_intr(): to check for ps_tq_active and to scheduling - ps_tq if ps_tq_active was 0. - * in ps_tq_int(): from the moment when we get ps_spinlock() to the - return, call of con() or scheduling ps_tq. - * in pi_schedule_claimed() when called from pi_do_claimed() called from - pd.c, everything until returning 1 or setting or setting ->claim_cont - on the path that returns 0 - * in pi_do_claimed() when called from pd.c, everything until the call - of pi_do_claimed() plus the everything until the call of cont() if - pi_do_claimed() has returned 1. - * in pi_wake_up() called for PIA that belongs to pd.c, everything from - the moment when pi_spinlock has been acquired. - -Lemma 2: - 1) at any time at most one thread of execution can be in that area or - be preempted there. - 2) When there is such a thread, pd_busy is set or pd_lock is held by - that thread. - 3) When there is such a thread, ps_tq_active is 0 or ps_spinlock is - held by that thread. - 4) When there is such a thread, all PIA belonging to pd.c have NULL - ->claim_cont or pi_spinlock is held by thread in question. - -Proof: consider the first moment when the above is not true. - -(1) can become not true if some thread enters that area while another is there. - a) do_pd_request1() can be called from next_request() or do_pd_request() - In the first case the thread was already in the area. In the second, - the thread was holding pd_lock and found pd_busy not set, which would - mean that (2) was already not true. - b) ps_set_intr() and pi_schedule_claimed() can be called only from the - area. - c) pi_do_claimed() is called by pd.c only from the area. - d) ps_tq_int() can enter the area only when the thread is holding - ps_spinlock and ps_tq_active is 1 (due to Lemma 1). It means that - (3) was already not true. - e) do_pd_{read,write}* could be called only from the area. The only - case that needs consideration is call from pi_wake_up() and there - we would have to be called for the PIA that got ->claimed_cont - from pd.c. That could happen only if pi_do_claimed() had been - called from pd.c for that PIA, which happens only for PIA belonging - to pd.c. - f) pi_wake_up() can enter the area only when the thread is holding - pi_spinlock and ->claimed_cont is non-NULL for PIA belonging to - pd.c. It means that (4) was already not true. - -(2) can become not true only when pd_lock is released by the thread in question. - Indeed, pd_busy is reset only in the area and thread that resets - it is holding pd_lock. The only place within the area where we - release pd_lock is in pd_next_buf() (called from within the area). - But that code does not reset pd_busy, so pd_busy would have to be - 0 when pd_next_buf() had acquired pd_lock. If it become 0 while - we were acquiring the lock, (1) would be already false, since - the thread that had reset it would be in the area simulateously. - If it was 0 before we tried to acquire pd_lock, (2) would be - already false. - -For similar reasons, (3) can become not true only when ps_spinlock is released -by the thread in question. However, all such places within the area are right -after resetting ps_tq_active to 0. - -(4) is done the same way - all places where we release pi_spinlock within -the area are either after resetting ->claimed_cont to NULL while holding -pi_spinlock, or after not tocuhing ->claimed_cont since acquiring pi_spinlock -also in the area. The only place where ->claimed_cont is made non-NULL is -in the area, under pi_spinlock and we do not release it until after leaving -the area. - -QED. - - -Corollary 1: ps_tq_active can be killed. Indeed, the only place where we -check its value is in ps_set_intr() and if it had been non-zero at that -point, we would have violated either (2.1) (if it was set while ps_set_intr() -was acquiring ps_spinlock) or (2.3) (if it was set when we started to -acquire ps_spinlock). - -Corollary 2: ps_spinlock can be killed. Indeed, Lemma 1 and Lemma 2 show -that the only possible contention is between scheduling ps_tq followed by -immediate release of spinlock and beginning of execution of ps_tq on -another CPU. - -Corollary 3: assignment to pd_busy in do_pd_read_start() and do_pd_write_start() -can be killed. Indeed, we are not holding pd_lock and thus pd_busy is already -1 here. - -Corollary 4: in ps_tq_int() uses of con can be replaced with uses of -ps_continuation, since the latter is changed only from the area. -We don't need to reset it to NULL, since we are guaranteed that there -will be a call of ps_set_intr() before we look at ps_continuation again. -We can remove the check for ps_continuation being NULL for the same -reason - the value is guaranteed to be set by the last ps_set_intr() and -we never pass it NULL. Assignements in the beginning of ps_set_intr() -can be taken to callers as long as they remain within the area. |