[src/trunk]: src/sys/dev/usb uhid(4): Omit needless softint indirection.

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/45a622509a2e
branches:  trunk
changeset: 957492:45a622509a2e
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Mon Nov 30 00:48:35 2020 +0000

description:
uhid(4): Omit needless softint indirection.

USB xfer callbacks already run in softint context at IPL_SOFTSERIAL,
and I see no reason why the call to psignal must happen instead at
the lower priority of IPL_SOFTCLOCK, so let's avoid using up the
scarce resource of softints for something that doesn't need 'em.

While here, use atomic_store_relaxed to update sc->sc_async and
atomic_load_relaxed to optimisitcally test it without acquiring
proc_lock.

diffstat:

 sys/dev/usb/uhid.c |  41 +++++++++++++++--------------------------
 1 files changed, 15 insertions(+), 26 deletions(-)

diffs (117 lines):

diff -r 84086d66abc2 -r 45a622509a2e sys/dev/usb/uhid.c
--- a/sys/dev/usb/uhid.c        Mon Nov 30 00:21:35 2020 +0000
+++ b/sys/dev/usb/uhid.c        Mon Nov 30 00:48:35 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: uhid.c,v 1.115 2020/11/29 22:54:51 riastradh Exp $     */
+/*     $NetBSD: uhid.c,v 1.116 2020/11/30 00:48:35 riastradh Exp $     */
 
 /*
  * Copyright (c) 1998, 2004, 2008, 2012 The NetBSD Foundation, Inc.
@@ -35,7 +35,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: uhid.c,v 1.115 2020/11/29 22:54:51 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: uhid.c,v 1.116 2020/11/30 00:48:35 riastradh Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_compat_netbsd.h"
@@ -138,7 +138,6 @@
 };
 
 Static void uhid_intr(struct uhidev *, void *, u_int);
-Static void uhid_softintr(void *);
 
 Static int uhid_do_read(struct uhid_softc *, struct uio *, int);
 Static int uhid_do_write(struct uhid_softc *, struct uio *, int);
@@ -180,7 +179,6 @@
        sc->sc_hdev.sc_intr = uhid_intr;
        sc->sc_hdev.sc_parent = uha->parent;
        sc->sc_hdev.sc_report_id = uha->reportid;
-       sc->sc_sih = softint_establish(SOFTINT_CLOCK, uhid_softintr, sc);
 
        uhidev_get_report_desc(uha->parent, &desc, &size);
        repid = uha->reportid;
@@ -277,7 +275,6 @@
        cv_destroy(&sc->sc_detach_cv);
        mutex_destroy(&sc->sc_lock);
        seldestroy(&sc->sc_rsel);
-       softint_disestablish(sc->sc_sih);
 
        return 0;
 }
@@ -304,26 +301,18 @@
        DPRINTFN(5, ("uhid_intr: waking %p\n", &sc->sc_q));
        cv_broadcast(&sc->sc_cv);
        selnotify(&sc->sc_rsel, 0, NOTE_SUBMIT);
-       if (sc->sc_async != NULL) {
-               DPRINTFN(3, ("uhid_intr: sending SIGIO %p\n", sc->sc_async));
-               softint_schedule(sc->sc_sih);
+       if (atomic_load_relaxed(&sc->sc_async) != NULL) {
+               mutex_enter(&proc_lock);
+               if (sc->sc_async != NULL) {
+                       DPRINTFN(3, ("uhid_intr: sending SIGIO to %jd\n",
+                               (intmax_t)sc->sc_async->p_pid));
+                       psignal(sc->sc_async, SIGIO);
+               }
+               mutex_exit(&proc_lock);
        }
        mutex_exit(&sc->sc_lock);
 }
 
-void
-uhid_softintr(void *cookie)
-{
-       struct uhid_softc *sc;
-
-       sc = cookie;
-
-       mutex_enter(&proc_lock);
-       if (sc->sc_async != NULL)
-                psignal(sc->sc_async, SIGIO);
-       mutex_exit(&proc_lock);
-}
-
 static int
 uhidopen(dev_t dev, int flag, int mode, struct lwp *l)
 {
@@ -367,7 +356,7 @@
 
        /* Paranoia: reset SIGIO before enabling interrputs.  */
        mutex_enter(&proc_lock);
-       sc->sc_async = NULL;
+       atomic_store_relaxed(&sc->sc_async, NULL);
        mutex_exit(&proc_lock);
 
        /* Open the uhidev -- after this point we can get interrupts.  */
@@ -390,7 +379,7 @@
        uhidev_close(&sc->sc_hdev);
 fail1: selnotify(&sc->sc_rsel, POLLHUP, 0);
        mutex_enter(&proc_lock);
-       sc->sc_async = NULL;
+       atomic_store_relaxed(&sc->sc_async, NULL);
        mutex_exit(&proc_lock);
        if (sc->sc_osize > 0) {
                kmem_free(sc->sc_obuf, sc->sc_osize);
@@ -429,7 +418,7 @@
 
        /* Reset SIGIO.  */
        mutex_enter(&proc_lock);
-       sc->sc_async = NULL;
+       atomic_store_relaxed(&sc->sc_async, NULL);
        mutex_exit(&proc_lock);
 
        /* Free the buffer and queue.  */
@@ -644,10 +633,10 @@
                                mutex_exit(&proc_lock);
                                return EBUSY;
                        }
-                       sc->sc_async = l->l_proc;
+                       atomic_store_relaxed(&sc->sc_async, l->l_proc);
                        DPRINTF(("uhid_do_ioctl: FIOASYNC %p\n", l->l_proc));
                } else
-                       sc->sc_async = NULL;
+                       atomic_store_relaxed(&sc->sc_async, NULL);
                mutex_exit(&proc_lock);
                break;