Changeset 026eb88

Timestamp:

03/19/10 14:33:17 (11 years ago)

Author:

Perry Lorier <perry@…>

Branches:

4.0.1-hotfixes, cachetimestamps, develop, dpdk-ndag, etsilive, getfragoff, help, libtrace4, master, ndag_format, pfring, rc-4.0.1, rc-4.0.2, rc-4.0.3, rc-4.0.4, ringdecrementfix, ringperformance, ringtimestampfixes

Children:

2b4316b

Parents:

d99c759

Message:

Make sure we write in multiples of 4k to keep O_DIRECT happy

File:

• lib/iow-stdio.c (modified) (4 diffs)

lib/iow-stdio.c

@@ -37 +37 @@
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/uio.h>
 #include <fcntl.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <string.h>
+#include <assert.h>
 
 /* Libtrace IO module implementing a standard IO writer, i.e. no decompression
  */
 
+enum { MIN_WRITE_SIZE = 4096 };
+
 struct stdiow_t {
+        char buffer[MIN_WRITE_SIZE];
+        int offset;
         int fd;
 };
@@ -52 +58 @@
 
 #define DATA(iow) ((struct stdiow_t *)((iow)->data))
+
+static int safe_open(const char *filename)
+{
+        int fd;
+/* Try opening with O_DIRECT */
+#ifdef O_DIRECT
+        fd = open(filename,
+                O_WRONLY
+                |O_CREAT
+                |O_TRUNC
+                |(force_directio_write?O_DIRECT:0),
+                0666);
+        if (fd != -1)
+                return fd;
+#endif
+/* If that failed (or we don't support O_DIRECT) try opening without */
+        fd = open(filename,
+                O_WRONLY
+                |O_CREAT
+                |O_TRUNC,
+                0666);
+        if (fd != -1)
+                return fd;
+        return fd;
+}
 
 iow_t *stdio_wopen(const char *filename)
@@ -61 +92 @@
         if (strcmp(filename,"-") == 0) 
                 DATA(iow)->fd = 1; /* STDOUT */
-        else
-                DATA(iow)->fd = open(filename,
-                                O_WRONLY
-                                |O_CREAT
-                                |O_TRUNC
-                                |(force_directio_write?O_DIRECT:0),
-                                0666);
+        else {
+                DATA(iow)->fd = safe_open(filename);
+        }
 
         if (DATA(iow)->fd == -1) {
@@ -74 +101 @@
         }
 
+        DATA(iow)->offset = 0;
+
         return iow;
 }
 
+#define min(a,b) ((a)<(b) ? (a) : (b))
+#define max(a,b) ((a)>(b) ? (a) : (b))
+/* Round A Down to the nearest multiple of B */
+#define rounddown(a,b) ((a)-((a)%b)
+
+/* When doing directio (O_DIRECT) we need to make sure that we write multiples of MIN_WRITE_SIZE.
+ * So we accumulate data into DATA(iow)->buffer, and write it out when we get at least MIN_WRITE_SIZE.
+ *
+ * Since most writes are likely to be larger than MIN_WRITE_SIZE optimise for that case.
+ */
 static off_t stdio_wwrite(iow_t *iow, const char *buffer, off_t len)
 {
-        return write(DATA(iow)->fd,buffer,len);
+        struct iovec iov[2];
+        int err;
+        /* Round down size to the nearest multiple of MIN_WRITE_SIZE */
+
+        assert(len >= 0);
+        
+        if (DATA(iow)->offset + len >= MIN_WRITE_SIZE) {
+                int amount;
+                iov[0].iov_base = DATA(iow)->buffer;
+                iov[0].iov_len = DATA(iow)->offset;
+                iov[1].iov_base = (void*)buffer; /* cast away constness, which is safe here */
+                iov[1].iov_len = len - (DATA(iow)->offset+len) % MIN_WRITE_SIZE;
+                err=writev(DATA(iow)->fd, iov, 2);
+                if (err==-1)
+                        return -1;
+                /* Drop off "err" bytes from the beginning of the buffers */
+                amount = min(DATA(iow)->offset, err);
+                DATA(iow)->offset -= amount;
+                err -= amount;
+                buffer += err;
+                len -= err;
+        }
+
+        /* Make sure we're not going to overflow the buffer.  The above writev should assure
+         * that this is true
+         */
+        assert(DATA(iow)->offset + len <= MIN_WRITE_SIZE);
+        assert(len >= 0);
+
+        /* Copy the remainder into the buffer to write next time. */
+        memcpy(DATA(iow)->buffer + DATA(iow)->offset, buffer, len);
+        DATA(iow)->offset += len;
+
+        return len;
 }
 
 static void stdio_wclose(iow_t *iow)
 {
+        long err;
+        /* Now, there might be some non multiple of the direct filesize left over, if so turn off
+         * O_DIRECT and write the final chunk.
+         */
+#ifdef O_DIRECT
+        err=fcntl(DATA(iow)->fd, F_GETFL);
+        if (err != -1 && (err & O_DIRECT) != 0) {
+                fcntl(DATA(iow)->fd,F_SETFL, err & ~O_DIRECT);
+        }
+        write(DATA(iow)->fd, DATA(iow)->buffer, DATA(iow)->offset);
+        DATA(iow)->offset = 0;
+#endif
         close(DATA(iow)->fd);
         free(iow->data);