Author: mjg Date: Sun May 24 03:50:49 2020 New Revision: 361429 URL: https://svnweb.freebsd.org/changeset/base/361429
Log: vfs: scale foffset_lock by using atomics instead of serializing on mtx pool Contending cases still serialize on sleepq (which would be taken anyway). Reviewed by: kib (previous version) Differential Revision: https://reviews.freebsd.org/D21626 Modified: head/sys/kern/vfs_vnops.c head/sys/sys/file.h Modified: head/sys/kern/vfs_vnops.c ============================================================================== --- head/sys/kern/vfs_vnops.c Sat May 23 23:38:35 2020 (r361428) +++ head/sys/kern/vfs_vnops.c Sun May 24 03:50:49 2020 (r361429) @@ -71,6 +71,7 @@ __FBSDID("$FreeBSD$"); #include <sys/resourcevar.h> #include <sys/rwlock.h> #include <sys/sx.h> +#include <sys/sleepqueue.h> #include <sys/sysctl.h> #include <sys/ttycom.h> #include <sys/conf.h> @@ -674,8 +675,9 @@ vn_rdwr_inchunks(enum uio_rw rw, struct vnode *vp, voi off_t foffset_lock(struct file *fp, int flags) { - struct mtx *mtxp; + volatile short *flagsp; off_t res; + short state; KASSERT((flags & FOF_OFFSET) == 0, ("FOF_OFFSET passed")); @@ -692,52 +694,66 @@ foffset_lock(struct file *fp, int flags) * According to McKusick the vn lock was protecting f_offset here. * It is now protected by the FOFFSET_LOCKED flag. */ - mtxp = mtx_pool_find(mtxpool_sleep, fp); - mtx_lock(mtxp); - if ((flags & FOF_NOLOCK) == 0) { - while (fp->f_vnread_flags & FOFFSET_LOCKED) { - fp->f_vnread_flags |= FOFFSET_LOCK_WAITING; - msleep(&fp->f_vnread_flags, mtxp, PUSER -1, - "vofflock", 0); + flagsp = &fp->f_vnread_flags; + if (atomic_cmpset_acq_16(flagsp, 0, FOFFSET_LOCKED)) + return (fp->f_offset); + + sleepq_lock(&fp->f_vnread_flags); + state = atomic_load_16(flagsp); + for (;;) { + if ((state & FOFFSET_LOCKED) == 0) { + if (!atomic_fcmpset_acq_16(flagsp, &state, + FOFFSET_LOCKED)) + continue; + break; } - fp->f_vnread_flags |= FOFFSET_LOCKED; + if ((state & FOFFSET_LOCK_WAITING) == 0) { + if (!atomic_fcmpset_acq_16(flagsp, &state, + state | FOFFSET_LOCK_WAITING)) + continue; + } + DROP_GIANT(); + sleepq_add(&fp->f_vnread_flags, NULL, "vofflock", 0, 0); + sleepq_wait(&fp->f_vnread_flags, PUSER -1); + PICKUP_GIANT(); + sleepq_lock(&fp->f_vnread_flags); + state = atomic_load_16(flagsp); } res = fp->f_offset; - mtx_unlock(mtxp); + sleepq_release(&fp->f_vnread_flags); return (res); } void foffset_unlock(struct file *fp, off_t val, int flags) { - struct mtx *mtxp; + volatile short *flagsp; + short state; KASSERT((flags & FOF_OFFSET) == 0, ("FOF_OFFSET passed")); -#if OFF_MAX <= LONG_MAX - if ((flags & FOF_NOLOCK) != 0) { - if ((flags & FOF_NOUPDATE) == 0) - fp->f_offset = val; - if ((flags & FOF_NEXTOFF) != 0) - fp->f_nextoff = val; - return; - } -#endif - - mtxp = mtx_pool_find(mtxpool_sleep, fp); - mtx_lock(mtxp); if ((flags & FOF_NOUPDATE) == 0) fp->f_offset = val; if ((flags & FOF_NEXTOFF) != 0) fp->f_nextoff = val; - if ((flags & FOF_NOLOCK) == 0) { - KASSERT((fp->f_vnread_flags & FOFFSET_LOCKED) != 0, - ("Lost FOFFSET_LOCKED")); - if (fp->f_vnread_flags & FOFFSET_LOCK_WAITING) - wakeup(&fp->f_vnread_flags); - fp->f_vnread_flags = 0; - } - mtx_unlock(mtxp); + +#if OFF_MAX <= LONG_MAX + if ((flags & FOF_NOLOCK) != 0) + return; +#endif + + flagsp = &fp->f_vnread_flags; + state = atomic_load_16(flagsp); + if ((state & FOFFSET_LOCK_WAITING) == 0 && + atomic_cmpset_rel_16(flagsp, state, 0)) + return; + + sleepq_lock(&fp->f_vnread_flags); + MPASS((fp->f_vnread_flags & FOFFSET_LOCKED) != 0); + MPASS((fp->f_vnread_flags & FOFFSET_LOCK_WAITING) != 0); + fp->f_vnread_flags = 0; + sleepq_broadcast(&fp->f_vnread_flags, SLEEPQ_SLEEP, 0, 0); + sleepq_release(&fp->f_vnread_flags); } void Modified: head/sys/sys/file.h ============================================================================== --- head/sys/sys/file.h Sat May 23 23:38:35 2020 (r361428) +++ head/sys/sys/file.h Sun May 24 03:50:49 2020 (r361429) @@ -163,7 +163,7 @@ struct fileops { * Below is the list of locks that protects members in struct file. * * (a) f_vnode lock required (shared allows both reads and writes) - * (f) protected with mtx_lock(mtx_pool_find(fp)) + * (f) updated with atomics and blocking on sleepq * (d) cdevpriv_mtx * none not locked */ _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "[email protected]"
