On 06.06.2011 18:38, Arne Jansen wrote:
On 06.06.2011 18:17, Ingo Molnar wrote:* Peter Zijlstra<peterz@xxxxxxxxxxxxx> wrote:On Mon, 2011-06-06 at 18:08 +0200, Ingo Molnar wrote:* Peter Zijlstra<peterz@xxxxxxxxxxxxx> wrote:On Mon, 2011-06-06 at 17:52 +0200, Ingo Molnar wrote:* Peter Zijlstra<peterz@xxxxxxxxxxxxx> wrote:Needs more staring at, preferably by someone who actually understands that horrid mess :/ Also, this all still doesn't make printk() work reliably while holding rq->lock.So, what about my suggestion to just *remove* the wakeup from there and use the deferred wakeup mechanism that klogd uses. That would make printk() *visibly* more robust in practice.That's currently done from the jiffy tick, do you want to effectively delay releasing the console_sem for the better part of a jiffy?Yes, and we already do it in some other circumstances.We do?Yes, see the whole printk_pending logic, it delays: wake_up_interruptible(&log_wait); to the next jiffies tick.Can you see any problem with that? klogd is an utter slowpath anyway.but console_sem isn't klogd. We delay klogd and that's perfectly fine, but afaict we don't delay console_sem.But console_sem is really a similar special case as klogd. See, it's about a *printk*. That's rare by definition. If someone on the console sees it he'll be startled by at least 10 msecs ;-) So delaying the wakeup to the next jiffy really fits into the same approach as we already do with&log_wait, hm?As long as it doesn't scramble the order of the messages, the delay imho doesn't matter even in very printk-heavy debugging sessions.
And, as important, doesn't reduce the throughput of printk. Having only100 wakeups/s sounds like the throughput is limited to 100xsizeof(ring buffer).
This would solve a real nightmare that has plagued us ever since printk() has done wakeups directly - i.e. like forever. Thanks, Ingo-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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