| Message ID | 20180724121753.5753-3-lbloch@janustech.com |
|---|---|
| State | New |
| Headers | show |
| Series | Introduction of l2-cache-full option for qcow2 images | expand |
On 07/24/2018 07:17 AM, Leonid Bloch wrote: > Signed-off-by: Leonid Bloch <lbloch@janustech.com> > --- > docs/qcow2-cache.txt | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/docs/qcow2-cache.txt b/docs/qcow2-cache.txt > index 8a09a5cc5f..a0a1267482 100644 > --- a/docs/qcow2-cache.txt > +++ b/docs/qcow2-cache.txt > @@ -97,9 +97,9 @@ need: > l2_cache_size = disk_size_GB * 131072 > refcount_cache_size = disk_size_GB * 32768 > > -QEMU has a default L2 cache of 1MB (1048576 bytes) and a refcount > -cache of 256KB (262144 bytes), so using the formulas we've just seen > -we have > +QEMU has a default L2 cache of 1MB (1048576 bytes) or 8 clusters (whichever > +is larger) and a refcount cache of 256KB (262144 bytes), so using the Looks suspicious; isn't the refcount cache size also dependent on the cluster size? > +formulas we've just seen we have (assuming the L2 cache is 1MB): > > 1048576 / 131072 = 8 GB of virtual disk covered by that cache > 262144 / 32768 = 8 GB >
On 07/24/2018 07:17 AM, Leonid Bloch wrote: > Signed-off-by: Leonid Bloch <lbloch@janustech.com> > --- > docs/qcow2-cache.txt | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) Updating the subject line, since this doc fix is appropriate for 3.0, if it is correct. > > diff --git a/docs/qcow2-cache.txt b/docs/qcow2-cache.txt > index 8a09a5cc5f..a0a1267482 100644 > --- a/docs/qcow2-cache.txt > +++ b/docs/qcow2-cache.txt > @@ -97,9 +97,9 @@ need: > l2_cache_size = disk_size_GB * 131072 > refcount_cache_size = disk_size_GB * 32768 > > -QEMU has a default L2 cache of 1MB (1048576 bytes) and a refcount > -cache of 256KB (262144 bytes), so using the formulas we've just seen > -we have > +QEMU has a default L2 cache of 1MB (1048576 bytes) or 8 clusters (whichever > +is larger) and a refcount cache of 256KB (262144 bytes), so using the > +formulas we've just seen we have (assuming the L2 cache is 1MB): > > 1048576 / 131072 = 8 GB of virtual disk covered by that cache > 262144 / 32768 = 8 GB >
On 07/24/2018 06:20 PM, Eric Blake wrote:
On 07/24/2018 07:17 AM, Leonid Bloch wrote:
Signed-off-by: Leonid Bloch [1]<lbloch@janustech.com>
---
docs/qcow2-cache.txt | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/docs/qcow2-cache.txt b/docs/qcow2-cache.txt
index 8a09a5cc5f..a0a1267482 100644
--- a/docs/qcow2-cache.txt
+++ b/docs/qcow2-cache.txt
@@ -97,9 +97,9 @@ need:
l2_cache_size = disk_size_GB * 131072
refcount_cache_size = disk_size_GB * 32768
-QEMU has a default L2 cache of 1MB (1048576 bytes) and a refcount
-cache of 256KB (262144 bytes), so using the formulas we've just
seen
-we have
+QEMU has a default L2 cache of 1MB (1048576 bytes) or 8 clusters
(whichever
+is larger) and a refcount cache of 256KB (262144 bytes), so using
the
Looks suspicious; isn't the refcount cache size also dependent on
the cluster size?
Yes, it's 4*cluster_size. But I realize now that the text here speaks
about the default sizes, which means with with 64KB clusters. So this
fix is not necessary. Will drop this patch.
+formulas we've just seen we have (assuming the L2 cache is 1MB):
1048576 / 131072 = 8 GB of virtual disk covered by that cache
262144 / 32768 = 8 GB
References
1. mailto:lbloch@janustech.com
diff --git a/docs/qcow2-cache.txt b/docs/qcow2-cache.txt index 8a09a5cc5f..a0a1267482 100644 --- a/docs/qcow2-cache.txt +++ b/docs/qcow2-cache.txt @@ -97,9 +97,9 @@ need: l2_cache_size = disk_size_GB * 131072 refcount_cache_size = disk_size_GB * 32768 -QEMU has a default L2 cache of 1MB (1048576 bytes) and a refcount -cache of 256KB (262144 bytes), so using the formulas we've just seen -we have +QEMU has a default L2 cache of 1MB (1048576 bytes) or 8 clusters (whichever +is larger) and a refcount cache of 256KB (262144 bytes), so using the +formulas we've just seen we have (assuming the L2 cache is 1MB): 1048576 / 131072 = 8 GB of virtual disk covered by that cache 262144 / 32768 = 8 GB
Signed-off-by: Leonid Bloch <lbloch@janustech.com> --- docs/qcow2-cache.txt | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)