Messages in this thread | | | From | Mark Salisbury <> | Subject | Re: No 100 HZ timer! | Date | Tue, 17 Apr 2001 08:12:11 -0400 |
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On Mon, 16 Apr 2001, you wrote: > Mark Salisbury wrote: > > > > > Given a system speed, there is a repeating timer rate which will consume > > > 100% of the system in handling the timer interrupts. An attempt will > > > be made to detect this rate and adjust the timer to prevent system > > > lockup. This adjustment will look like timer overruns to the user > > > (i.e. we will take a percent of the interrupts and record the untaken > > > interrupts as overruns) > > > > just at first blush, there are some things in general but I need to read > > this again and more closely.... > > > > but, with POSIX timers, there is a nifty little restriction/protection built > > into the spec regarding the re-insertion of short interval repeating timers. > > that is: a repeating timer will not be re-inserted until AFTER the > > associated signal handler has been handled. > > Actually what it says is: "Only a single signal shall be queued to the > process for a given timer at any point in time. When a timer for which > a signal is still pending expires, no signal shall be queued, and a > timer overrun shall occur." > > It then goes on to talk about the overrun count and how it is to be > managed. > I guess I was confusing what the spec said with the way in which I chose to comply with the spec. I calculate overruns (I know when a timer went off, and how many of its intervals have passed since it went off by by time_since_expire/interval) and don't reinsert until return from the signal handler.
this prevents a flood of high frequency interrupts inherently and allows processing of the signal handlers to proceed cleanly.
-- /*------------------------------------------------** ** Mark Salisbury | Mercury Computer Systems ** ** mbs@mc.com | System OS - Kernel Team ** **------------------------------------------------** ** I will be riding in the Multiple Sclerosis ** ** Great Mass Getaway, a 150 mile bike ride from ** ** Boston to Provincetown. Last year I raised ** ** over $1200. This year I would like to beat ** ** that. If you would like to contribute, ** ** please contact me. ** **------------------------------------------------*/
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