Re: [Qemu-devel] [PATCH 0/6] Configure metadata overlap checks at runtime

[Max Reitz]

On 2013-09-20 10:37, Max Reitz wrote:
> This series changes the way of selecting what metadata overlap checks to
> perform from (currently) using a macro to using a variable contained in
> BDRVQcowState which can be configured at runtime through several command
> line options.
>
> Although this does not seem necessary anymore regarding performance
> (because I could not find any performance hits using cached overlap
> checks), it seems cleaner to me this way.
>
> This series depends on:
>   - qcow2: Correct snapshots size for overlap check
>
> Max Reitz (6):
>    qcow2: Use negated overflow check mask
>    qcow2: Make overlap check mask variable
>    qcow2: Add overlap-check options
>    qcow2: Array assigning options to OL check bits
>    qcow2: Add more overlap check bitmask macros
>    qcow2: Evaluate overlap check options
>
>   block/qcow2-cache.c    |  8 ++---
>   block/qcow2-cluster.c  | 16 ++++-----
>   block/qcow2-refcount.c | 22 ++++++------
>   block/qcow2-snapshot.c | 12 +++----
>   block/qcow2.c          | 93 +++++++++++++++++++++++++++++++++++++++++++++++---
>   block/qcow2.h          | 30 ++++++++++++----
>   6 files changed, 137 insertions(+), 44 deletions(-)

Ping – does anyone have comments on this series?

It doesn't really seem to be required, since the current default setting 
is fast enough (although I still have to do a performance test regarding 
the host CPU usage). However, this series introduces a cleaner interface 
to the overlap checks besides the option to change the overlap checks at 
startup (which isn't just useful to users, but also a requirement for 
I/O tests on overlap checks on inactive L1 tables).

Max