X-Git-Url: http://git.annexia.org/?a=blobdiff_plain;f=2019-kvm-forum%2F4500-new-qemu-flag.html;h=ea729bba1ba870dd4636e7e4100d2cddd6f5b364;hb=6f34bcd5178f2622d9a15915ad2ca136525f318a;hp=98324718c259759fa44e10dd95c05e835ed1441f;hpb=600b60e5bb802212c001505be3bc0f85305bfd48;p=libguestfs-talks.git
diff --git a/2019-kvm-forum/4500-new-qemu-flag.html b/2019-kvm-forum/4500-new-qemu-flag.html
index 9832471..ea729bb 100644
--- a/2019-kvm-forum/4500-new-qemu-flag.html
+++ b/2019-kvm-forum/4500-new-qemu-flag.html
@@ -5,51 +5,17 @@
The fix: raise the victory flag
- Filler text - need a graphic here showing multiple combinations:
+ QEMU 4.0 added BDRV_REQ_NO_FALLBACK to detect if
+ zeroing is fast, and automatically utilizes it during 'qemu-img
+ convert':
+
+ - No support for flag: avoid pre-zeroing
+
- Flag supported and succeeds (for O(1) implementation):
+ pre-zeroing is a win
+
- Flag supported but fails (for O(n) implementation): no penalty
+ from pre-zeroing
+
-
[WZ] = WRITE_ZEROES, normal
-
[FZ+] = WRITE_ZEROES, successful with FAST_ZERO flag
-
[FZ-] = WRITE_ZEROES, fails with FAST_ZERO flag
-
[W...] = WRITE for data
-
-
- O(1) server O(n) server
-pre-patch [W...][WZ][W...][WZ] [W...][WZ..][W...][WZ..]
-
-with fast zero [FZ+][W...][W...] [FZ-][W...][WZ..][W...][WZ..]
- (faster) (marginally slower)
-
-
-Or maybe a graph of demo results:
-
- | B
- 12|
- |
- |
- |
- |
- |
- |
- | A B
- 8 | B B B
- |
- |
- |
- t |
- i |
- m |
- e | A A
- 4 | A A
- |
- |
- |
- |
- |
- |
- |
- 0 +----------------------------------------------------------------
- just WRITE WRITE_ZEROES blind FAST_ZERO FAST_ZERO
- on every hole pre-zeroing missing supported
-
+