Messages in this thread |  | | Date | Fri, 22 Jan 2021 23:52:39 +0000 | Subject | Issue in dmesg time with lockless ring buffer | From | "J. Avila" <> |
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Hello,
When doing some internal testing on a 5.10.4 kernel, we found that the time taken for dmesg seemed to increase from the order of milliseconds to the order of seconds when the dmesg size approached the ~1.2MB limit. After doing some digging, we found that by reverting all of the patches in printk/ up to and including 896fbe20b4e2333fb55cc9b9b783ebcc49eee7c7 ("use the lockless ringbuffer"), we were able to once more see normal dmesg times.
This kernel had no meaningful diffs in the printk/ dir when compared to Linus' tree. This behavior was consistently reproducible using the following steps:
1) In one shell, run "time dmesg > /dev/null" 2) In another, constantly write to /dev/kmsg
Within ~5 minutes, we saw that dmesg times increased to 1 second, only increasing further from there. Is this a known issue?
Thank you,
Avila
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