On 2024-08-22 12:32:15 [-0400], Derek Barbosa wrote: > Hi, Hi, > TLDR: plain, vanilla 6.11.0-0.rc3 is slower on flush and > does not print traces in panic/crash context consistently. Thank you for testing. > For the stock kernel, we observed an average of about 14,263 messages printed > within 30 seconds. The standard deviation here hovers at around 1.52 messages, > with a variance of 2.3 messages. > > For the "new printk" kernel, we observed an average of about 12,693 messages > printed within 30 seconds. The standard devation here hovers at about 131.2 > messages, with a variance of 17211 messages. > > We observe a rough 12-13 percent overall delta between new printk and the > stock kernel in this test case, with a larger disparity in standard > deviation/variance. I am a bit confused. You write here ~14k messages within 30secs for "stock" aka 6.11.0-0.rc3 and then ~12k messages for "new printk" aka from the latest RT tree. At the top you write "6.11.0-0.rc3 is slower on flush". This means something else I guess. Regarding your RCU stall: You stuff a _lot_ into the printk buffer. And then printk is forced print everything out in a single sitting. The whole printing job is done within a preempt_disable region so RCU has to wait until it is done. If printing of the whole buffer takes >60sec then you see your RCU stall. The current RT tree will do the printing from a kthread which remains preemptible because your printing threads don't print any errors/ panics for 30seconds. So RCU gets its turn. Sebastian
