Hello, try to use .unlocked_ioctl instead of .ioctl for your drivers file_operations struct. Andreas > -----Original Message----- > From: linux-rt-users-owner@xxxxxxxxxxxxxxx [mailto:linux-rt-users- > owner@xxxxxxxxxxxxxxx] On Behalf Of Claus Gindhart > Sent: Wednesday, January 28, 2009 8:34 AM > To: linux-rt-users@xxxxxxxxxxxxxxx; Gerd Koenig; Peter Widmann > Cc: klaus weschmann; Jochen Beier > Subject: Realtime capability of ioctl() vs. read() and write() > > I am running a Linux 2.6.24.7-rt21 Kernel on our HW. > > This HW contains a number of IO-Ports, and the drivers for these IO- > Ports are > designed in a way, that various ioctl() function provide the interface > to > these Ports. > > Now, i recognized, that processes, which are using such ioctl()'s, > absolutely > do not run in realtime (regardless on the priority). If i cat a huge > file to > a /dev/ttyX device, the process jitters for many milliseconds. > > This does NOT happen, if i modify the driver and the user space process > to > access IO's via read() and write() instead of ioctl()'s. > > My question is: Is it a known and intended behaviour, that ioctl()'s > ruin > realtime behaviour, and that IO's should only be accessed via read() > and > write() ? > I didnt find any documentation, which would advice me not to use > ioctl() in > realtime applications. > > -- > Mit freundlichen Gruessen / Best regards > > Claus Gindhart > SW R&D > Kontron Modular Computers > phone :++49 (0)8341-803-374 > mailto:claus.gindhart@xxxxxxxxxxxxxxxxxxx > http://www.kontron.com > -- > To unsubscribe from this list: send the line "unsubscribe linux-rt- > users" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html
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