Consume with mmap if enabled
authorJulien Desfossez <julien.desfossez@polymtl.ca>
Wed, 29 Jun 2011 21:03:24 +0000 (17:03 -0400)
committerDavid Goulet <david.goulet@polymtl.ca>
Thu, 30 Jun 2011 15:03:58 +0000 (11:03 -0400)
Signed-off-by: Julien Desfossez <julien.desfossez@polymtl.ca>
kconsumerd/kconsumerd.c

index d14f68b4c2d87e5f2c166efed49ac41667f68ba8..c816d0dece14e623ebdf3d68b60d68b3ae443466 100644 (file)
@@ -35,6 +35,7 @@
 #include <urcu/list.h>
 #include <poll.h>
 #include <unistd.h>
+#include <sys/mman.h>
 
 #include "lttngerr.h"
 #include "libkernelctl.h"
@@ -239,6 +240,119 @@ static int set_signal_handler(void)
        return ret;
 }
 
+/*
+ * on_read_subbuffer_mmap
+ *
+ * mmap the ring buffer, read it and write the data to the tracefile.
+ * Returns the number of bytes written
+ */
+static int on_read_subbuffer_mmap(struct ltt_kconsumerd_fd *kconsumerd_fd,
+               unsigned long len)
+{
+       unsigned long mmap_len;
+       unsigned long mmap_offset;
+       unsigned long padded_len;
+       unsigned long padding_len;
+       char *mmap_base;
+       char *padding = NULL;
+       long ret = 0;
+       off_t orig_offset = kconsumerd_fd->out_fd_offset;
+       int fd = kconsumerd_fd->consumerd_fd;
+       int outfd = kconsumerd_fd->out_fd;
+
+       /* get the padded subbuffer size to know the padding required */
+       ret = kernctl_get_padded_subbuf_size(fd, &padded_len);
+       if (ret != 0) {
+               ret = errno;
+               perror("kernctl_get_padded_subbuf_size");
+               goto end;
+       }
+       padding_len = padded_len - len;
+       padding = malloc(padding_len * sizeof(char));
+       memset(padding, '\0', padding_len);
+
+       /* get the len of the mmap region */
+       ret = kernctl_get_mmap_len(fd, &mmap_len);
+       if (ret != 0) {
+               ret = errno;
+               perror("kernctl_get_mmap_len");
+               goto end;
+       }
+
+       /* get the offset inside the fd to mmap */
+       ret = kernctl_get_mmap_read_offset(fd, &mmap_offset);
+       if (ret != 0) {
+               ret = errno;
+               perror("kernctl_get_mmap_read_offset");
+               goto end;
+       }
+
+       mmap_base = mmap(NULL, mmap_len, PROT_READ, MAP_PRIVATE, fd, mmap_offset);
+       if (mmap_base == MAP_FAILED) {
+               perror("Error mmaping");
+               ret = -1;
+               goto end;
+       }
+
+       while (len > 0) {
+               ret = write(outfd, mmap_base, len);
+               if (ret >= len) {
+                       len = 0;
+               } else if (ret < 0) {
+                       ret = errno;
+                       perror("Error in file write");
+                       goto end;
+               }
+               /* This won't block, but will start writeout asynchronously */
+               sync_file_range(outfd, kconsumerd_fd->out_fd_offset, ret,
+                               SYNC_FILE_RANGE_WRITE);
+               kconsumerd_fd->out_fd_offset += ret;
+       }
+
+       /* once all the data is written, write the padding to disk */
+       ret = write(outfd, padding, padding_len);
+       if (ret < 0) {
+               ret = errno;
+               perror("Error writing padding to file");
+               goto end;
+       }
+
+       /*
+        * This does a blocking write-and-wait on any page that belongs to the
+        * subbuffer prior to the one we just wrote.
+        * Don't care about error values, as these are just hints and ways to
+        * limit the amount of page cache used.
+        */
+       if (orig_offset >= kconsumerd_fd->max_sb_size) {
+               sync_file_range(outfd, orig_offset - kconsumerd_fd->max_sb_size,
+                               kconsumerd_fd->max_sb_size,
+                               SYNC_FILE_RANGE_WAIT_BEFORE
+                               | SYNC_FILE_RANGE_WRITE
+                               | SYNC_FILE_RANGE_WAIT_AFTER);
+               /*
+                * Give hints to the kernel about how we access the file:
+                * POSIX_FADV_DONTNEED : we won't re-access data in a near
+                * future after we write it.
+                * We need to call fadvise again after the file grows because
+                * the kernel does not seem to apply fadvise to non-existing
+                * parts of the file.
+                * Call fadvise _after_ having waited for the page writeback to
+                * complete because the dirty page writeback semantic is not
+                * well defined. So it can be expected to lead to lower
+                * throughput in streaming.
+                */
+               posix_fadvise(outfd, orig_offset - kconsumerd_fd->max_sb_size,
+                               kconsumerd_fd->max_sb_size, POSIX_FADV_DONTNEED);
+       }
+       goto end;
+
+end:
+       if (padding != NULL) {
+               free(padding);
+       }
+       return ret;
+}
+
 /*
  * on_read_subbuffer
  *
@@ -355,22 +469,46 @@ static int read_subbuffer(struct ltt_kconsumerd_fd *kconsumerd_fd)
                goto end;
        }
 
-       /* read the whole subbuffer */
-       err = kernctl_get_padded_subbuf_size(infd, &len);
-       if (err != 0) {
-               ret = errno;
-               perror("Getting sub-buffer len failed.");
-               goto end;
-       }
+       if (DEFAULT_CHANNEL_OUTPUT == LTTNG_KERNEL_SPLICE) {
+               /* read the whole subbuffer */
+               err = kernctl_get_padded_subbuf_size(infd, &len);
+               if (err != 0) {
+                       ret = errno;
+                       perror("Getting sub-buffer len failed.");
+                       goto end;
+               }
 
-       /* splice the subbuffer to the tracefile */
-       ret = on_read_subbuffer(kconsumerd_fd, len);
-       if (ret < 0) {
-               /*
-                * display the error but continue processing to try
-                * to release the subbuffer
-                */
-               ERR("Error splicing to tracefile");
+               /* splice the subbuffer to the tracefile */
+               ret = on_read_subbuffer(kconsumerd_fd, len);
+               if (ret < 0) {
+                       /*
+                        * display the error but continue processing to try
+                        * to release the subbuffer
+                        */
+                       ERR("Error splicing to tracefile");
+               }
+       } else if (DEFAULT_CHANNEL_OUTPUT == LTTNG_KERNEL_MMAP) {
+               /* read the used subbuffer size */
+               err = kernctl_get_subbuf_size(infd, &len);
+               if (err != 0) {
+                       ret = errno;
+                       perror("Getting sub-buffer len failed.");
+                       goto end;
+               }
+
+               /* write the subbuffer to the tracefile */
+               ret = on_read_subbuffer_mmap(kconsumerd_fd, len);
+               if (ret < 0) {
+                       /*
+                        * display the error but continue processing to try
+                        * to release the subbuffer
+                        */
+                       ERR("Error writing to tracefile");
+               }
+       } else {
+               ERR("Unknown output method");
+               ret = -1;
+               goto end;
        }
 
        err = kernctl_put_next_subbuf(infd);
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