Arrange to align shared disk buffers on at least 32-byte boundaries,

not just MAXALIGN boundaries.  This makes a noticeable difference in
the speed of transfers to and from kernel space, at least on recent
Pentiums, and might help other CPUs too.  We should look at making
this happen for local buffers and buffile.c too.  Patch from Manfred Spraul.

diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index f2bdc3eb91dbffb05889d21442ec9d439444d7a9..0b80e0585ec58ad090e28241d977ee0a9b0cdbd0 100644 (file)
--- a/src/backend/storage/ipc/shmem.c
+++ b/src/backend/storage/ipc/shmem.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/storage/ipc/shmem.c,v 1.70 2003/08/04 02:40:03 momjian Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/storage/ipc/shmem.c,v 1.71 2003/09/21 17:57:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -131,6 +131,7 @@ InitShmemAllocation(void *seghdr)
 void *
 ShmemAlloc(Size size)
 {
+       uint32          newStart;
        uint32          newFree;
        void       *newSpace;
 
@@ -146,10 +147,16 @@ ShmemAlloc(Size size)
 
        SpinLockAcquire(ShmemLock);
 
-       newFree = shmemseghdr->freeoffset + size;
+       newStart = shmemseghdr->freeoffset;
+
+       /* extra alignment for large requests, since they are probably buffers */
+       if (size >= BLCKSZ)
+               newStart = BUFFERALIGN(newStart);
+
+       newFree = newStart + size;
        if (newFree <= shmemseghdr->totalsize)
        {
-               newSpace = (void *) MAKE_PTR(shmemseghdr->freeoffset);
+               newSpace = (void *) MAKE_PTR(newStart);
                shmemseghdr->freeoffset = newFree;
        }
        else

diff --git a/src/include/c.h b/src/include/c.h
index 02d47bfe4617b9e015cef3d031f91e3a455ea672..934e976803cd541e7ae81c7082429114ac0f2f97 100644 (file)
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -12,7 +12,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: c.h,v 1.152 2003/08/04 02:40:10 momjian Exp $
+ * $Id: c.h,v 1.153 2003/09/21 17:57:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -522,13 +522,16 @@ typedef NameData *Name;
  * ----------------
  */
 
-#define TYPEALIGN(ALIGNVAL,LEN) (((long)(LEN) + (ALIGNVAL-1)) & ~(ALIGNVAL-1))
+#define TYPEALIGN(ALIGNVAL,LEN)  \
+       (((long) (LEN) + (ALIGNVAL-1)) & ~((long) (ALIGNVAL-1)))
 
 #define SHORTALIGN(LEN)                        TYPEALIGN(ALIGNOF_SHORT, (LEN))
 #define INTALIGN(LEN)                  TYPEALIGN(ALIGNOF_INT, (LEN))
 #define LONGALIGN(LEN)                 TYPEALIGN(ALIGNOF_LONG, (LEN))
 #define DOUBLEALIGN(LEN)               TYPEALIGN(ALIGNOF_DOUBLE, (LEN))
 #define MAXALIGN(LEN)                  TYPEALIGN(MAXIMUM_ALIGNOF, (LEN))
+/* MAXALIGN covers only built-in types, not buffers */
+#define BUFFERALIGN(LEN)               TYPEALIGN(ALIGNOF_BUFFER, (LEN))
 
 
 /* ----------------------------------------------------------------

diff --git a/src/include/pg_config_manual.h b/src/include/pg_config_manual.h
index 451ef351e65a767fc37243af1670dde58afb7e3d..98d357760dc7b03a1b2de4013a0adc506be23aa9 100644 (file)
--- a/src/include/pg_config_manual.h
+++ b/src/include/pg_config_manual.h
@@ -6,7 +6,7 @@
  * for developers.     If you edit any of these, be sure to do a *full*
  * rebuild (and an initdb if noted).
  *
- * $Id: pg_config_manual.h,v 1.5 2003/08/04 00:43:29 momjian Exp $
+ * $Id: pg_config_manual.h,v 1.6 2003/09/21 17:57:21 tgl Exp $
  *------------------------------------------------------------------------
  */
 
@@ -126,6 +126,14 @@
  */
 #define BITS_PER_BYTE          8
 
+/*
+ * Preferred alignment for disk I/O buffers.  On some CPUs, copies between
+ * user space and kernel space are significantly faster if the user buffer
+ * is aligned on a larger-than-MAXALIGN boundary.  Ideally this should be
+ * a platform-dependent value, but for now we just hard-wire it.
+ */
+#define ALIGNOF_BUFFER 32
+
 /*
  * Disable UNIX sockets for those operating system.
  */