On Sun, Jan 12, 2020 at 06:09:10AM +0000, Mateusz Guzik wrote:
> Author: mjg
> Date: Sun Jan 12 06:09:10 2020
> New Revision: 356656
> URL: https://svnweb.freebsd.org/changeset/base/356656
>
> Log:
> Add "panicked" boolean which can be tested instead of panicstr
>
> The test is performed all the time and reading entire panicstr to do it
> wastes space.
What space does it waste ? The space in the read-mostly section ?
And what is the difference between reading a pointer vs. reading a byte ?
CPU still has to read the whole cache line.
>
> Modified:
> head/sys/kern/kern_shutdown.c
> head/sys/sys/systm.h
>
> Modified: head/sys/kern/kern_shutdown.c
> ==============================================================================
> --- head/sys/kern/kern_shutdown.c Sun Jan 12 06:07:54 2020
> (r356655)
> +++ head/sys/kern/kern_shutdown.c Sun Jan 12 06:09:10 2020
> (r356656)
> @@ -217,7 +217,8 @@ SYSCTL_INT(_kern, OID_AUTO, kerneldump_gzlevel, CTLFLA
> * Variable panicstr contains argument to first call to panic; used as flag
> * to indicate that the kernel has already called panic.
> */
> -const char __read_mostly *panicstr;
> +const char *panicstr;
> +bool __read_frequently panicked;
>
> int __read_mostly dumping; /* system is dumping */
> int rebooting; /* system is rebooting */
> @@ -873,6 +874,7 @@ vpanic(const char *fmt, va_list ap)
> else {
> bootopt |= RB_DUMP;
> panicstr = fmt;
> + panicked = true;
> newpanic = 1;
> }
>
>
> Modified: head/sys/sys/systm.h
> ==============================================================================
> --- head/sys/sys/systm.h Sun Jan 12 06:07:54 2020 (r356655)
> +++ head/sys/sys/systm.h Sun Jan 12 06:09:10 2020 (r356656)
> @@ -53,7 +53,8 @@ extern int cold; /* nonzero if we are doing a
> cold bo
> extern int suspend_blocked; /* block suspend due to pending shutdown */
> extern int rebooting; /* kern_reboot() has been called. */
> extern const char *panicstr; /* panic message */
> -#define KERNEL_PANICKED() __predict_false(panicstr != NULL)
> +extern bool panicked;
> +#define KERNEL_PANICKED() __predict_false(panicked)
> extern char version[]; /* system version */
> extern char compiler_version[]; /* compiler version */
> extern char copyright[]; /* system copyright */
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