[libvirt] [PATCH RFC] iohelper: Introduces a small sleep do avoid hunging other tasks

[Leonardo Bras]

While dumping very large VMs (over 128GB), iohelper seems to cause
very intense IO usage on the disk, and it causes some processes
(like journald) to hung, and depending on kernel configuration,
to panic.

This change creates a time window, after every 10GB written, so
this processes can write to the disk, and avoid hunging.

Signed-off-by: Leonardo Bras <leonardo at linux.ibm.com>
---
 src/util/iohelper.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/util/iohelper.c b/src/util/iohelper.c
index ddc338b7c7..164c1e2085 100644
--- a/src/util/iohelper.c
+++ b/src/util/iohelper.c
@@ -52,6 +52,8 @@ runIO(const char *path, int fd, int oflags)
     unsigned long long total = 0;
     bool direct = O_DIRECT && ((oflags & O_DIRECT) != 0);
     off_t end = 0;
+    const unsigned long long sleep_step = (long long)10*1024*1024*1024;
+    unsigned long long next_sleep = sleep_step;
 
 #if HAVE_POSIX_MEMALIGN
     if (posix_memalign(&base, alignMask + 1, buflen)) {
@@ -128,6 +130,12 @@ runIO(const char *path, int fd, int oflags)
 
         total += got;
 
+        /* sleeps for a while to avoid hunging other tasks */
+        if (total > next_sleep) {
+            next_sleep += sleep_step;
+            usleep(100*1000);
+        }
+
         /* handle last write size align in direct case */
         if (got < buflen && direct && fdout == fd) {
             ssize_t aligned_got = (got + alignMask) & ~alignMask;
-- 
2.20.1