A performance optimization, inspired by a conversation with Thor Simon:
- Keep a freelist of component buffer headers, defaulting to 8 headers per component (tunable with the CCDNBUF kernel compile option). - When allocating a component buffer, try to pull a header off the freelist first, falling back on MALLOC() if the freelist is empty. Use MALLOC() rather than malloc(), because it will attempt to short-cut the allocation before actually making a full-blown malloc() call. - Keep statistics on how many component buffer headers have been allocated and how many of those allocations have resulted in freelist misses. With these changes, I observed measurable decreases in system and wall clock time on operations on an 8G ccd, as well as a measurable drop in the time spent in ccdbuffer() (measured with kernel profiling).
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thorpej
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@ -1,7 +1,7 @@
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/* $NetBSD: ccd.c,v 1.37 1997/01/30 03:32:56 thorpej Exp $ */
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/* $NetBSD: ccd.c,v 1.38 1997/01/30 04:00:52 thorpej Exp $ */
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/*-
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* Copyright (c) 1996 The NetBSD Foundation, Inc.
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* Copyright (c) 1996, 1997 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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@ -132,14 +132,46 @@ struct ccdbuf {
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int cb_unit; /* target unit */
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int cb_comp; /* target component */
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int cb_flags; /* misc. flags */
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#define CBF_MIRROR 0x01 /* we're for a mirror component */
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LIST_ENTRY(ccdbuf) cb_list; /* entry on freelist */
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};
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#define getccdbuf() \
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((struct ccdbuf *)malloc(sizeof(struct ccdbuf), M_DEVBUF, M_WAITOK))
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#define putccdbuf(cbp) \
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free((caddr_t)(cbp), M_DEVBUF)
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/* cb_flags */
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#define CBF_MIRROR 0x01 /* we're for a mirror component */
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/*
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* Number of freelist buffers per component. Overridable in kernel
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* config file and patchable.
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*/
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#ifndef CCDNBUF
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#define CCDNBUF 8
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#endif
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int ccdnbuf = CCDNBUF;
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/*
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* XXX Is it OK to wait here?
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* XXX maybe set up a timeout when we hit some lowater?
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* XXX --thorpej
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*/
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#define CCDGETBUF(cs, cbp) do { \
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(cs)->sc_ngetbuf++; \
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if (((cbp) = (cs)->sc_freelist.lh_first) != NULL) { \
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LIST_REMOVE((cbp), cb_list); \
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(cs)->sc_freecount--; \
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} else { \
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(cs)->sc_nmisses++; \
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MALLOC((cbp), struct ccdbuf *, \
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sizeof(struct ccdbuf), M_DEVBUF, M_WAITOK); \
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} \
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} while (0)
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#define CCDPUTBUF(cs, cbp) do { \
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if ((cs)->sc_freecount == (cs)->sc_hiwat) { \
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FREE((cbp), M_DEVBUF); \
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} else { \
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LIST_INSERT_HEAD(&(cs)->sc_freelist, (cbp), cb_list); \
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(cs)->sc_freecount++; \
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} \
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} while (0)
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#define CCDLABELDEV(dev) \
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(MAKEDISKDEV(major((dev)), ccdunit((dev)), RAW_PART))
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@ -221,6 +253,7 @@ ccdinit(ccd, cpaths, p)
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struct partinfo dpart;
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struct ccdgeom *ccg = &cs->sc_geom;
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char tmppath[MAXPATHLEN];
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struct ccdbuf *cbp;
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int error;
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#ifdef DEBUG
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@ -410,6 +443,23 @@ ccdinit(ccd, cpaths, p)
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ccg->ccg_nsectors = 1024 * (1024 / ccg->ccg_secsize);
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ccg->ccg_ncylinders = cs->sc_size / ccg->ccg_nsectors;
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/*
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* Allocate the component buffer header freelist. We allocate
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* ccdnbuf buffers per component.
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*/
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LIST_INIT(&cs->sc_freelist);
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cs->sc_hiwat = cs->sc_nccdisks * ccdnbuf;
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cs->sc_freecount = cs->sc_hiwat;
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for (ix = 0; ix < cs->sc_hiwat; ix++) {
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MALLOC(cbp, struct ccdbuf *, sizeof(struct ccdbuf),
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M_DEVBUF, M_WAITOK);
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LIST_INSERT_HEAD(&cs->sc_freelist, cbp, cb_list);
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}
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/* Reset statistics. */
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cs->sc_nmisses = 0;
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cs->sc_ngetbuf = 0;
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cs->sc_flags |= CCDF_INITED;
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cs->sc_cflags = ccd->ccd_flags; /* So we can find out later... */
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cs->sc_unit = ccd->ccd_unit;
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@ -808,7 +858,7 @@ ccdbuffer(cs, bp, bn, addr, bcount, cbpp)
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/*
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* Fill in the component buf structure.
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*/
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cbp = getccdbuf();
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CCDGETBUF(cs, cbp);
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cbp->cb_flags = 0;
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cbp->cb_buf.b_flags = bp->b_flags | B_CALL;
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cbp->cb_buf.b_iodone = ccdiodone;
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@ -847,7 +897,7 @@ ccdbuffer(cs, bp, bn, addr, bcount, cbpp)
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*/
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if ((cs->sc_cflags & CCDF_MIRROR) &&
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((cbp->cb_buf.b_flags & B_READ) == 0)) {
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cbp = getccdbuf();
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CCDGETBUF(cs, cbp);
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*cbp = *cbpp[0];
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cbp->cb_flags = CBF_MIRROR;
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cbp->cb_buf.b_dev = ci2->ci_dev; /* XXX */
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@ -924,7 +974,7 @@ ccdiodone(vbp)
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}
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count = cbp->cb_buf.b_bcount;
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cbflags = cbp->cb_flags;
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putccdbuf(cbp);
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CCDPUTBUF(cs, cbp);
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/*
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* If all done, "interrupt".
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@ -1014,6 +1064,7 @@ ccdioctl(dev, cmd, data, flag, p)
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struct ccd_softc *cs;
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struct ccd_ioctl *ccio = (struct ccd_ioctl *)data;
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struct ccddevice ccd;
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struct ccdbuf *cbp;
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char **cpp;
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struct vnode **vpp;
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@ -1165,6 +1216,12 @@ ccdioctl(dev, cmd, data, flag, p)
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free(cs->sc_cinfo[i].ci_path, M_DEVBUF);
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}
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/* Free component buffer freelist. */
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while ((cbp = cs->sc_freelist.lh_first) != NULL) {
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LIST_REMOVE(cbp, cb_list);
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FREE(cbp, M_DEVBUF);
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}
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/* Free interleave index. */
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for (i = 0; cs->sc_itable[i].ii_ndisk; ++i)
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free(cs->sc_itable[i].ii_index, M_DEVBUF);
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@ -1,7 +1,7 @@
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/* $NetBSD: ccdvar.h,v 1.11 1996/02/28 01:08:32 thorpej Exp $ */
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/* $NetBSD: ccdvar.h,v 1.12 1997/01/30 04:00:53 thorpej Exp $ */
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/*-
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* Copyright (c) 1996 The NetBSD Foundation, Inc.
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* Copyright (c) 1996, 1997 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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@ -78,6 +78,8 @@
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* @(#)cdvar.h 8.1 (Berkeley) 6/10/93
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*/
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#include <sys/queue.h>
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/*
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* Dynamic configuration and disklabel support by:
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* Jason R. Thorpe <thorpej@nas.nasa.gov>
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@ -174,6 +176,8 @@ struct ccdgeom {
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u_int32_t ccg_ncylinders; /* # cylinders per unit */
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};
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struct ccdbuf;
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/*
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* A concatenated disk is described after initialization by this structure.
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*/
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@ -189,6 +193,13 @@ struct ccd_softc {
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struct ccdgeom sc_geom; /* pseudo geometry info */
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char sc_xname[8]; /* XXX external name */
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struct disk sc_dkdev; /* generic disk device info */
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LIST_HEAD(, ccdbuf) sc_freelist; /* component buffer freelist */
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int sc_freecount; /* number of entries */
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int sc_hiwat; /* freelist high water mark */
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/* Statistics */
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u_long sc_nmisses; /* number of freelist misses */
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u_long sc_ngetbuf; /* number of ccdbuf allocs */
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};
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/* sc_flags */
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