On Fri, Feb 12, 2016 at 10:09:39AM +0100, Premysl Kouril wrote: > > Except for the last the backtraces you're showing are for futex locks, > > which are not used by the kernel, but some user process. So the locking > > problem is somewhere in the user space setup (perhaps in qemu). > > This would indicate your ext4 set up is not the same as LVM. > > Setup on the qemu/kvm is exactly the same (same test box, same command > line arguments execept for the argument for the virtual machine disk > which reference LVM volume or EXT4 based file) You mentioned using qcow; if you're using qcow, than the userspace qemu/kvm process will need to do its own locking to manage its own space management file. In general, if you need to do allocation management, either because you are writing to a sparse file, and ext4 has to do block allocation, or if you are writing to a fallocated file, and ext4 has to keep track of whether a block has been written to that location before (and if not, do a journalled transaction to clear the unwritten bit), there will be extra work that has to be done at the qcow or ext4 layer that doesn't have to be done at the LVM layer. Of course, this work is providing extra services (such as space management and/or not revealing previously written block contents from another customer to your current customer's VM, which might make your local data protection authorities cranky). So the devil is very much in the details of how you set up the hypervisor, and "except for the argument for the virtual machine disk" is leaving an awful lot unspecified. Whether you preallocated and pre-zeroed the file can make a difference, whether you are using buffered or direct I/O based on the cache parameter makes a difference, etc., etc. Cheers, - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
