ethernet: Reduce a runtime ntohs() in fast path

[zlei]

Summary

For untagged traffic, we always hit the check for ether_type.

No functional change intended.

MFC after: 1 week

[zlei]

sys/net/if_ethersubr.c

633

An extra space to improve readability.

[melifaro]

I’d rather avoid doing that. ntohs is fast and branchless, so I’d vote for optimizing for readability here (unless there is a measurable performance gain)

[zlei]

In D42389#967281, @melifaro wrote:

I’d rather avoid doing that.
ntohs is fast and branchless,

True indeed.

so I’d vote for optimizing for readability here (unless there is a measurable performance gain)

No measurable performance gain.

[cy]

In D42389#967281, @melifaro wrote:

I’d rather avoid doing that. ntohs is fast and branchless, so I’d vote for optimizing for readability here (unless there is a measurable performance gain)

Agrreed.

sys/net/if_ethersubr.c

SYSCTL_INT(_kern, OID_AUTO, kerneldump_gzlevel, CTLFLAG_RWTUN,
     "Kernel crash dump compression level");
 
 /*
  * Variable panicstr contains argument to first call to panic; used as flag
  * to indicate that the kernel has already called panic.
  */
 const char *panicstr __read_mostly;
 
-int __read_mostly dumping;                /* system is dumping */
-int rebooting;                                /* system is rebooting */
+int dumping __read_mostly;                /* system is dumping */
+int rebooting __read_mostly;                /* system is rebooting */
 /*
  * Used to serialize between sysctl kern.shutdown.dumpdevname and list
  * modifications via ioctl.
  */
 static struct mtx dumpconf_list_lk;
 MTX_SYSINIT(dumper_configs, &dumpconf_list_lk, "dumper config list", MTX_DEF);
 
 /* Our selected dumper(s). */