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devclass_alloc_unit: move "at" hint test to after device-in-use test

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Only perform this expensive operation when the unit number is a
potential candidate (i.e. not already in use), thereby reducing device
scan time on systems with many devices, unit numbers, and drivers.

Sponsored by:	NetApp, Inc.
Sponsored by:	Klara, Inc.
X-NetApp-PR:	#61
Differential Revision:	https://reviews.freebsd.org/D31381
This commit is contained in:
Adam Fenn 2021-08-02 11:27:17 -05:00 committed by Kyle Evans
parent 9f1db6c555
commit 8ca384eb1d
1 changed files with 4 additions and 4 deletions
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8
sys/kern/subr_bus.c
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@ -1638,15 +1638,15 @@ devclass_alloc_unit(devclass_t dc, device_t dev, int *unitp)
/* Unwired device, find the next available slot for it */
unit = 0;
for (unit = 0;; unit++) {
/* If this device slot is already in use, skip it. */
if (unit < dc->maxunit && dc->devices[unit] != NULL)
continue;
/* If there is an "at" hint for a unit then skip it. */
if (resource_string_value(dc->name, unit, "at", &s) ==
0)
continue;
/* If this device slot is already in use, skip it. */
if (unit < dc->maxunit && dc->devices[unit] != NULL)
continue;
break;
}
}