backend: fix switch_ioscheduler()

The backend.c function switch_ioscheduler() suffers from several
problems:
1) This function only considers the first file of a job. For jobs using
   multiple files, the ioscheduler switch will done only for that file.
2) If the job file is a character device, a pipe or a regular file for
   which the hosting block device file cannot be determined (e.g. a
   remote file), thring to switch the IO scheduler causes a crash as the
   file disk_util field is NULL.
Fix both problems by introducing the helper function set_ioscheduler()
and changing switch_ioscheduler() to repeatdly call this helper for all
files of the job, ignoring character device files, pipe files and files
without a hosting device information.

Also update the man page to better explain when the ioscheduler option
applies.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/backend.c b/backend.c
index 52b4ca7e1c83e8feda885a8d3d84219f5f784190..399c299e14aa6f518502e02cf94f1def7e713403 100644 (file)
--- a/backend.c
+++ b/backend.c
@@ -1341,22 +1341,19 @@ int init_io_u_buffers(struct thread_data *td)
        return 0;
 }
 
+#ifdef FIO_HAVE_IOSCHED_SWITCH
 /*
- * This function is Linux specific.
+ * These functions are Linux specific.
  * FIO_HAVE_IOSCHED_SWITCH enabled currently means it's Linux.
  */
-static int switch_ioscheduler(struct thread_data *td)
+static int set_ioscheduler(struct thread_data *td, struct fio_file *file)
 {
-#ifdef FIO_HAVE_IOSCHED_SWITCH
        char tmp[256], tmp2[128], *p;
        FILE *f;
        int ret;
 
-       if (td_ioengine_flagged(td, FIO_DISKLESSIO))
-               return 0;
-
-       assert(td->files && td->files[0]);
-       sprintf(tmp, "%s/queue/scheduler", td->files[0]->du->sysfs_root);
+       assert(file->du && file->du->sysfs_root);
+       sprintf(tmp, "%s/queue/scheduler", file->du->sysfs_root);
 
        f = fopen(tmp, "r+");
        if (!f) {
@@ -1417,11 +1414,55 @@ static int switch_ioscheduler(struct thread_data *td)
 
        fclose(f);
        return 0;
+}
+
+static int switch_ioscheduler(struct thread_data *td)
+{
+       struct fio_file *f;
+       unsigned int i;
+       int ret = 0;
+
+       if (td_ioengine_flagged(td, FIO_DISKLESSIO))
+               return 0;
+
+       assert(td->files && td->files[0]);
+
+       for_each_file(td, f, i) {
+
+               /* Only consider regular files and block device files */
+               switch (f->filetype) {
+               case FIO_TYPE_FILE:
+               case FIO_TYPE_BLOCK:
+                       /*
+                        * Make sure that the device hosting the file could
+                        * be determined.
+                        */
+                       if (!f->du)
+                               continue;
+                       break;
+               case FIO_TYPE_CHAR:
+               case FIO_TYPE_PIPE:
+               default:
+                       continue;
+               }
+
+               ret = set_ioscheduler(td, f);
+               if (ret)
+                       return ret;
+       }
+
+       return 0;
+}
+
 #else
+
+static int switch_ioscheduler(struct thread_data *td)
+{
        return 0;
-#endif
 }
 
+#endif /* FIO_HAVE_IOSCHED_SWITCH */
+
 static bool keep_running(struct thread_data *td)
 {
        unsigned long long limit;

diff --git a/fio.1 b/fio.1
index c59a80020bf25f0ff035f09bd3c4a5c31168fc1f..18dc156ad027471b8d11083158c21688c610d93d 100644 (file)
--- a/fio.1
+++ b/fio.1
@@ -690,7 +690,8 @@ of how that would work.
 .TP
 .BI ioscheduler \fR=\fPstr
 Attempt to switch the device hosting the file to the specified I/O scheduler
-before running.
+before running. If the file is a pipe, a character device file or if device
+hosting the file could not be determined, this option is ignored.
 .TP
 .BI create_serialize \fR=\fPbool
 If true, serialize the file creation for the jobs. This may be handy to