March 2015 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Re: Profiling processes in Linux kernel
by Malte Vesper March 25, 2015

March 25, 2015

On 25/03/15 15:51, Sreejith M M wrote: > On Wed, Mar 25, 2015 at 8:50 PM, Malte Vesper > <malte.vesper(a)postgrad.manchester.ac.uk> wrote: >> On 25/03/15 15:08, Sreejith M M wrote: >>> Hi All, >>> >>> I would like to know if there is anyway to profile thread running time >>> in linux kernel? >>> If there is already some method for it, please share. >>> Otherwise, let me know where to start looking >>> >>> >>> >> perf or oprofile should do the job. So far I only used perf to profile a >> driver so far. Be aware that you have to enable the profiling options >> when compiling your kernel. > can you share a good tutorial or starting point to understand and use > these tools? > > > Google is your friend, I had some success with following instructions a bloke called Brendan Gregg, who seems to be a profiling guru, wrote: http://www.brendangregg.com/linuxperf.html

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Profiling processes in Linux kernel
by Sreejith M M March 25, 2015

March 25, 2015

Hi All, I would like to know if there is anyway to profile thread running time in linux kernel? If there is already some method for it, please share. Otherwise, let me know where to start looking -- Thanks, Sreejith

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Writing driver for a net device which does not support interrupt
by Freeman Zhang March 24, 2015

March 24, 2015

Hi list, I'm writing a net device driver for my final project in college. But the half-finished device doesn't support interrupt yet(those hardware guys...) So I'm wondering if there is some way to poll the device for its status and events. Google tells me 'NAPI' uses a polling mechanism, but it still needs hardware interrupt support :( Any suggestions? Thanks Freeman

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Fwd: Kernelnewbies Digest, Vol 52, Issue 41
by Vishwas Srivastava March 24, 2015

March 24, 2015

---------- Forwarded message ---------- From: <kernelnewbies-request(a)kernelnewbies.org> Date: Mon, Mar 23, 2015 at 9:30 PM Subject: Kernelnewbies Digest, Vol 52, Issue 41 To: kernelnewbies(a)kernelnewbies.org Send Kernelnewbies mailing list submissions to kernelnewbies(a)kernelnewbies.org To subscribe or unsubscribe via the World Wide Web, visit http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies or, via email, send a message with subject or body 'help' to kernelnewbies-request(a)kernelnewbies.org You can reach the person managing the list at kernelnewbies-owner(a)kernelnewbies.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Kernelnewbies digest..." Today's Topics: 1. Re: Delaying an interrupt handler (Daniel Baluta) 2. Re: Sysfs requirement for running generic_buffer.c application - IIO sensors (Daniel Baluta) 3. Re: Delaying an interrupt handler (Milton Krutt) 4. Re: Get Back Into Kernel Work (el_es) 5. Re: Sysfs requirement for running generic_buffer.c application - IIO sensors (s.rawat) 6. Re: Get Back Into Kernel Work (Nicholas Krause) 7. Re: Writing driver for a net device which does not support interrupt (Valdis.Kletnieks(a)vt.edu) ---------------------------------------------------------------------- Message: 1 Date: Mon, 23 Mar 2015 14:46:51 +0200 From: Daniel Baluta <daniel.baluta(a)gmail.com> Subject: Re: Delaying an interrupt handler To: Milton Krutt <milton(a)krutt.org> Cc: Kernelnewbies <kernelnewbies(a)kernelnewbies.org> Message-ID: <CAEnQRZDQrnNjxKtDSqmmA%2BQFHYJbXoWWE%3DcHEPVE7LOLHA31Uw(a)mail.gmail.com> Content-Type: text/plain; charset=UTF-8 On Mon, Mar 23, 2015 at 2:18 PM, Milton Krutt <milton(a)krutt.org> wrote: > Hi. > It is known that no semaphore synchronization should be > used inside an interrupt handler. > > Anyway, I am looking at a freeBSD device driver (written by > a profesionist) and there are semaphores inside an interrupt > handler's subroutine. > > Since I should port to linux that driver, I ask you how can I > reach such synchronization under linux; I tried to use semaphores > inside my handler but I got complains, and I don't want to break > the law, so no semaphores for me. Perhaps spinlocks could be the solution :). 2.6.10 please no - :), Linux kernel is now at 4.0. Daniel. Hi Daniel, Its us legitimate to use semaphore inside the interrupt handler but the only thing what should not be done is to _acquire_ it from within. Releasing is perfectly all right. By the way what is done within the interrupt handler in the code written by professional? release ?? acquire?? Vishwas ------------------------------ Message: 2 Date: Mon, 23 Mar 2015 15:40:39 +0200 From: Daniel Baluta <daniel.baluta(a)gmail.com> Subject: Re: Sysfs requirement for running generic_buffer.c application - IIO sensors To: "s.rawat" <imsaurabhrawat(a)gmail.com> Cc: "linux-iio(a)vger.kernel.org" <linux-iio(a)vger.kernel.org>, kernelnewbies <kernelnewbies(a)kernelnewbies.org> Message-ID: <CAEnQRZDmYTzZPyMiO%3D0SMo%3Dd1k3s_Dj-T7u7Jw696dz1c5uRJA(a)mail.gmail.com> Content-Type: text/plain; charset=UTF-8 On Mon, Mar 23, 2015 at 7:27 AM, s.rawat <imsaurabhrawat(a)gmail.com> wrote: > I have two system having different kernel version and drivers(IIO) on which > i can run the generic_buffer.c application .On one system it works fine but > on the other it does not give the input reports data. What kernel versions are you using? Why are you using different drivers? :D thanks, Daniel. ------------------------------ Message: 3 Date: Mon, 23 Mar 2015 06:46:23 -0700 From: Milton Krutt <milton(a)krutt.org> Subject: Re: Delaying an interrupt handler To: kernelnewbies(a)kernelnewbies.org Message-ID: <20150323134622.GA4933@debian> Content-Type: text/plain; charset=us-ascii > On Mon, Mar 23, 2015 at 2:18 PM, Milton Krutt <milton(a)krutt.org> wrote: > > Hi. > > It is known that no semaphore synchronization should be > > used inside an interrupt handler. > > > > Anyway, I am looking at a freeBSD device driver (written by > > a profesionist) and there are semaphores inside an interrupt > > handler's subroutine. > > > > Since I should port to linux that driver, I ask you how can I > > reach such synchronization under linux; I tried to use semaphores > > inside my handler but I got complains, and I don't want to break > > the law, so no semaphores for me. > > Perhaps spinlocks could be the solution :). > > 2.6.10 please no - :), Linux kernel is now at 4.0. > > Daniel. Yes and no. The routine the int. handler's delay depends on has to make some non atomic work. So if I lock a spinlock and then I do some "lengthy" (i.e. non atomic) job, then I get a warning message like "spinlock held while being preempted" (or similar). In symbols, you suggest something like process P{ spin_lock(lock); non_atomic_function(); spin_unlock(lock); } int. handler { spin_lock(lock); do_things(); /* preferably atomically */ spin_unlock(lock); } My first attempt is still to avoid both semaphores and the above remedy, in order to delay the int. handler up to a desired point. Thanks! ------------------------------ Message: 4 Date: Mon, 23 Mar 2015 13:51:30 +0000 (UTC) From: el_es <el.es.cr(a)gmail.com> Subject: Re: Get Back Into Kernel Work To: kernelnewbies(a)kernelnewbies.org Message-ID: <loom.20150323T144133-770(a)post.gmane.org> Content-Type: text/plain; charset=us-ascii Nicholas Krause <xerofoify <at> gmail.com> writes: > > I have listened to peoples feedback. Am I still missing something > as I now do > 1. Build test all patches > 2. Reading the code properly > 3.Testing my patches > 4.Listening to feedback > Nick > [trim] Insert this: X. Do My Own Research First, THEN ask questions preferably at X = 0, 2, 4, 6, 8 of the above list. Read a few netiquette/'how to write questions smart' manuals to learn how to let people /know/ you did your research. If your school work gets in the way though, it probably means it's much more important and you should not miss it. Cheers, CHSMBIDWT/MSPANC. el es ------------------------------ Message: 5 Date: Mon, 23 Mar 2015 20:22:30 +0530 From: "s.rawat" <imsaurabhrawat(a)gmail.com> Subject: Re: Sysfs requirement for running generic_buffer.c application - IIO sensors To: Daniel Baluta <daniel.baluta(a)gmail.com> Cc: "linux-iio(a)vger.kernel.org" <linux-iio(a)vger.kernel.org>, kernelnewbies <kernelnewbies(a)kernelnewbies.org> Message-ID: <CALwa49t7WB_KhE5o7d%3DB3vJXwd%2B%3DctwU0_Rv6j93uHK5665F0A(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" kernel version is 3.10.20 , drivers are hid-sensor-* driver. (hid-accel-3d,hid-gyro-3d,etc.) for different sensors.I have two different devices having two different kernels,Just wanted to know the difference technically why one is not working. On Mon, Mar 23, 2015 at 7:10 PM, Daniel Baluta <daniel.baluta(a)gmail.com> wrote: > On Mon, Mar 23, 2015 at 7:27 AM, s.rawat <imsaurabhrawat(a)gmail.com> wrote: > > I have two system having different kernel version and drivers(IIO) on > which > > i can run the generic_buffer.c application .On one system it works fine > but > > on the other it does not give the input reports data. > > What kernel versions are you using? Why are you using different drivers? :D > > thanks, > Daniel. >

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Eudyptula challenge
by sahil aggarwal March 24, 2015

March 24, 2015

Hi all, I am on task5, little says to read ch 14 (device model) of LDD3 but ch 13 (USB driver) seems to be the one i should read. I have already been following this book and reached ch5, would it be ok to jump to ch 13/14 directly.? Moreover reading /Documentation/usb/hotplug.txt seems to help me solving the challenge. So should i read ch 13/14 of continue reading in order.? Thanks Regards

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apparent sleep
by Milton Krutt March 23, 2015

March 23, 2015

Hi. Following LDD3, I am dealing with wait queues, on a 2.6.10. My loop is like: while(enough()){ prepare_to_wait(&queue_head, &queue_entry, TASK_INTERRUPTIBLE); atomic_set(&flag, 0); if (!atomic_read(&flag, 0)) schedule(); finish_wait(&queue_head, &queue_entry); } My intention is to wake up the process at each loop by issuing CTRL^D. Here is what happens: the first time the process yields the processor, it actually sleeps and I have to give it a CTRL^D in order to put it again in running state; unfortunately, in the following loops, although it calls the schedule() function, it magically regains the processor putting hisself in a running state (since it runs, I guess the state is a running one). In a few words, the while loop has thousands of iterations, but CTRL^D is needed only during the first one. Thank you all

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Get Back Into Kernel Work
by nick March 23, 2015

March 23, 2015

Greetings All, After my terrible results before and getting banned from the list due to these results, I am wondering if there is any work in the USB or Networking Subsystem I can start with. Further more recently I read Essential Kernel Drivers so I have some idea of how to write drivers now and want to get my feet wet. In addition if I am still not trusted yet,that's OK too. :) Thanks, Nick

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Delaying an interrupt handler
by Milton Krutt March 23, 2015

March 23, 2015

Hi. It is known that no semaphore synchronization should be used inside an interrupt handler. Anyway, I am looking at a freeBSD device driver (written by a profesionist) and there are semaphores inside an interrupt handler's subroutine. Since I should port to linux that driver, I ask you how can I reach such synchronization under linux; I tried to use semaphores inside my handler but I got complains, and I don't want to break the law, so no semaphores for me. The scenario is the following: firmware downloader { while(fw_blocks--){ /* the call below will cause an interrupt */ load_block(); /* sleep unitl the int handler ackn's the previous operation, and prevent ANY int. handler operations until the process goes actually to sleep through the following call */ sleep(); } } int handler { if(the process is NOT asleep) wait(); wake up the process. } NOTE: I am on a 2.6.10 in order to be closely tutored by LDD3.

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a good video about programming and software engg in Linux kernel
by Anuz Pratap Singh Tomar March 23, 2015

March 23, 2015

Hello folks, This video was shared by Alison to me. Here Dave Chinner talks about some of the recent events which transpired at lkml and kernelnewbies. I think we all have witness the said event and some of us have participated in this so called flame war. Besides all that, this is a very good video which every kernel newbie should watch. Infact I am going to point this to anyone who asks the basic questions like, "I want to be kernel haxor, what do I do?". Feel free to share and propagate https://www.youtube.com/watch?v=VpuVDfSXs-g -- Thank you Warm Regards Anuz

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LXC/cgroups process group scheduling in linux 3.18+
by Nobin Mathew March 23, 2015

March 23, 2015

Hi, Apologises if I am asking a dump question. Is there any support for container(lxc/cgroups) scheduling in linux scheduler(3.18+). I want to use only unprivileged containers. Basically I want to give more priority to processes in a container(basically to app in the container). Can we use RT scheduling?. one more question is how process scheduling happens inside the container(lxc/cgroups), is it like for some time(till the next container is selected), only processes inside container(lxc/cgroups) is scheduled? Thanks

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