Messages in this thread | | | Date | Tue, 19 Sep 2023 15:31:02 -0600 | Subject | Re: [PATCH v1] arch/x86: port I/O tracing on x86 | From | Dan Raymond <> |
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On 9/19/2023 3:12 PM, Peter Zijlstra wrote: >>> This means I can no longer use early_console->write() to print to my >>> early_serial_console. >> >> Why not? Did you try it? > > I have tried debugging the kernel for the last 15+ years. The only > reliable way to get something out of the machine is outb on the serial > port. Anything else is a waste of time.. > > Adding tracing to it (which relies on RCU, which might not be alive at > this point) which might itself be the problem, is a total no-go. > > You do not wreck early_serial_console.
But you didn't try my patch to see if it "wrecks" early_serial_console. I doubt it has any impact there because it does not get compiled into boot code. Notice the BOOT_COMPRESSED_MISC_H and BOOT_BOOT_H checks.
I don't understand your general objection. The kernel already has tracing for memory mapped I/O which includes serial ports. This patch just extends that to include port I/O.
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