On Fri, Aug 3, 2012 at 3:36 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > On Fri, Aug 03, 2012 at 03:25:17PM -0700, Pandita, Vikram wrote: >> >> This was something that got used internally and helped at times. >> > >> > Could you have used the trace point instead? >> >> As i understood the trace_prink(), one would need to modify existing >> printk -> trace_printk. Is my understanding correct? > > No, you should just be able to watch the tracepoint, right? yes. Assumption being you know _EXACTLY_ what code piece to watch for. Which may not be the case all times. > >> Most of the times the problem exhibits as a random hang, without having a clue >> which code to modify. That time one generic defconfig global switch is >> your first tool. >> >> Other issue i found, using this patch, that on multi-core ARM systems, >> almost 99% of times, IRQ's are handled by CPU0, >> even if CPU0 was really busy and other CPU's were free. I am yet to >> understand a good reason why. > > Can't you see that from /proc/interrupts today? You are right that was the next step i did and that shows the problem as well. The point i was trying to make, with printk showing cpu-id, there are problems in system that could get highlighted, given printk almost always runs with linux kernel. > >> this patch also helped in other areas as mentioned in the thread >> http://marc.info/?l=linux-omap&m=134401269106619&w=2 > > I still don't understand how adding the cpu number to printk enabled you > to find any problem like this. Can't you just add the cpu number to the > printk messages you care about for your specific hardware? > The assumption here is that a developer knows well enough, which code to modify for logging. I my experience, that is not true most of the times. A global defconfig switch is much easier to enable. Eg: when i have some timing related issue, first thing i go for is to enable PRINTK_TIME, without even having to think about the erring code. Then time-stamps lead to bad code. That is the same though process behind the cpu-id in printk. > greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
