Date: Wed, 26 Feb 2020 12:15:33 +0530 From: Arpan Palit <babupalit@gmail.com> To: Ian Lepore <ian@freebsd.org> Cc: freebsd-hackers@freebsd.org, freebsd-questions@freebsd.org Subject: Re: msleep_spin is failed to waken up even after wakeup routine is invoked for the same. Message-ID: <CAF3txfjatPDaBEtR-aYWzzQnKMsv4rrQ6WYEQ=AB-VYv4sqxHA@mail.gmail.com> In-Reply-To: <08fd4dcf7231237abf749834d6bce006892eac26.camel@freebsd.org> References: <CAF3txfi6Kz1y0a8jusGKrYFyMAER60xpkngQS0m-%2BY9G1RX5cw@mail.gmail.com> <890a299c074fc83a02911583531d686257924be8.camel@freebsd.org> <CAF3txfh0G%2BVkCHptXcDvu_KUCzP6yEWinSw8LXa4KLB1e-mT3A@mail.gmail.com> <08fd4dcf7231237abf749834d6bce006892eac26.camel@freebsd.org>
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Thanks for the clarification Ian. The issue is not happening now. I have ran the test for more than 1000 iterations multiple times now, but looks like some device specific internal issue has come up, working on it. If I need any more help in future, I hope I can ask you again. Thanks again for the quick response. -Arpan On Mon, Feb 24, 2020 at 1:18 AM Ian Lepore <ian@freebsd.org> wrote: > On Sun, 2020-02-23 at 12:30 +0530, Arpan Palit wrote: > > Thanks for replying Ian. > > > > The code is similar to the fix structure code as you have mentioned > above. > > > > Its happening after running the test for 5 to 10 iterations, out of 2k > > posted command to the hardware only 1 or 2 of them are failing to wake > > up properly. mutex lock has been properly introduced in both > > wait_for_completion code & interrupt handler part and also the doneflag > is > > getting set from the interrupt context properly. > > > > I am running 16 thread of 2k command simultaneously. > > > > I have verified that from the hardware side the command completion is > > proper, its failing in waking up the sleep in software side. > > > > So I am suspecting some issue with the scheduler which failed to wake up > > the sleep in this case. > > > > Below is the current code structure: > > > > /* Wait for Completion */ > > mtx_lock(cmd_comp_lock); > > completion = false; > > ret = execute_cmd(cmd); > > if (ret == 0) { > > while ( !completion && err == 0) > > err = msleep(cmd, cmd_comp_lock, PCATCH, "cmd_xfer", hz); > > } > > mtx_unlock(cmd_comp_lock); > > > > /* Interrupt handler */ > > mtx_lock_spin(cmd_lock); > > *//Disable inerrupt > > *// error checks > > completion = true; > > wakeup_one(cmd); > > mtx_unlock_spin(cmd_lock); > > *//Enable interrupt > > > > That shows two different mutexes being used, which violates the safe > pattern for doing conditional wakeups. The same mutex that protects > the setting of the 'completion' variable in the interrupt handler must > be used to protect the clearing and testing of that variable in the > mainline code, to avoid missed wakeups. That means using msleep_spin() > with cmd_lock in the mainline code. > > -- Ian > > > > > On Wed, Feb 19, 2020 at 8:12 PM Ian Lepore <ian@freebsd.org> wrote: > > > > > On Wed, 2020-02-19 at 14:13 +0530, Arpan Palit wrote: > > > > Hi, > > > > > > > > I am facing one issue where wakeup rountine call is unable to > > > > waken up a > > > > msleep_spin routine call with a timeout value of 10 Seconds. > > > > > > > > The real scenario is as follows: post a hardware command and > > > > sleep using > > > > msleep_spin routine till interrupt comes, After getting the > > > > interrupt > > > > > > waken > > > > up the sleeping process using wakeup_one/wakeup routine call. As > > > > there > > > > > > are > > > > more than 2048 command and 16 parallel threads are running, > > > > observed randomly *one or two of the posted command* is *timing > > > > out* for > > > > which the *interrupt has came and also wakeup routine is invoked > > > > *after > > > > getting the interrupt for the same command. > > > > > > > > Note: > > > > *The issue is not seen when number of commands are less than 2048 > > > > with > > > > timeout of 10 seconds. > > > > *The issue can be seen with less number of commands also when > > > > timeout > > > > > > value > > > > 1 second. > > > > > > > > Can anyone please provide me an optimized way to schedule the > > > > process or > > > > > > a > > > > better way to do the scheduling. > > > > > > > > Thanks, > > > > Arpan Palit > > > > > > > > > > Is there any chance this is the classic "missed wakeup" scenario, > > > where > > > the wakeup happens before the thread enters msleep_spin()? That > > > can > > > happen with code structured like > > > > > > enqueue_request(req); > > > err = msleep_spin(req, etc); > > > /* Handle done req or timeout */ > > > > > > and a fix is to structure the code using the same idiom required > > > for > > > pthread_cond_wait() in userland, something like: > > > > > > req->doneflag = false; > > > enqueue_request(req); > > > while (!req->doneflag && err == 0) > > > err = msleep_spin(req, etc); > > > /* Handle done req or timeout */ > > > > > > and of course on the interrupt handler side you need something like > > > > > > /* lock mutex, do hardware stuff */ > > > req->doneflag = true; > > > wakeup(req); > > > /* unlock mutex */ > > > > > > -- Ian > > > > > > > > > > > > > _______________________________________________ > > freebsd-hackers@freebsd.org mailing list > > https://lists.freebsd.org/mailman/listinfo/freebsd-hackers > > To unsubscribe, send any mail to " > > freebsd-hackers-unsubscribe@freebsd.org" > >
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