Hi Bart Thanks for your kindly response. On 04/20/2018 10:11 PM, Bart Van Assche wrote: > On Fri, 2018-04-20 at 14:55 +0800, jianchao.wang wrote: >> Hi Bart >> >> On 04/20/2018 12:43 AM, Bart Van Assche wrote: >>> Use the deadline instead of the request generation to detect whether >>> or not a request timer fired after reinitialization of a request >> >> Maybe use deadline to do this is not suitable. >> >> Let's think of the following scenario. >> >> T1/T2 times in nano seconds >> J1/J2 times in jiffies >> >> rq is started at T1,J1 >> blk_mq_timeout_work >> -> blk_mq_check_expired >> -> save rq->__deadline (J1 + MQ_RQ_IN_FLIGHT) >> >> rq is completed and freed >> rq is allocated and started again on T2 >> rq->__deadline = J2 + MQ_RQ_IN_FLIGHT >> -> synchronize srcu/rcu >> -> blk_mq_terminate_expired >> -> rq->__deadline (J2 + MQ_RQ_IN_FLIGHT) >> >> 1. deadline = rq->__deadline & ~RQ_STATE_MASK (0x3) >> if J2-J1 < 4 jiffies, we will get the same deadline value. >> >> 2. even if we do some bit shift when save and get deadline >> if T2 - T1 < time of 1 jiffies, we sill get the same deadline. > > Hello Jianchao, > > How about using the upper 16 or 32 bits of rq->__deadline to store a generation > number? I don't know any block driver for which the product of (deadline in > seconds) and HZ exceeds (1 << 32). > yes, we don't need so long timeout value. However, req->__deadline is an absolute time, not a relative one, its type is unsigned long variable which is same with jiffies. If we reserve some bits (not just 1 or 2 bits) of req->__deadline for generation number, how to handle it when mod_timer ? Thanks Jianchao
