Re: [Xen-devel] tapdisk in debian 3.11 kernel

[Fabio Fantoni <fabio.fantoni@xxxxxxx>]

I advise you to try qdisk instead of blktap, the performance increasing is very big.
With systems such as windows that uses the disk even when it could use a lot of ram still free, the difference is clearly visible.

Here one screenshot of benkmark when I switch from blktap2 of debian package to qdisk of upstream qemu some months ago:
http://lists.xen.org/archives/html/xen-devel/2013-07/jpgV4ajjhOQ11.jpg

I did the benkmark on windows 7 with your gplpv.

2013/12/7 James Harper <james.harper@xxxxxxxxxxxxxxxx>

I can't get tapdisk to run after upgrading to 3.11 (wheezy-backports). strace tells me it is failing on the call to io_setup with EINVAL.

The man page for io_setup tells me that ctx_idp parameter should be initialised to 0, and EINVAL means ctx_idp is not initialised. Looking at the code for tapdisk, it appears to initialise ctx_idp to 1, with a comment:

/*
 * We used a kernel patch to return an fd associated with the AIO context
 * so that we can concurrently poll on synchronous and async descriptors.
 * This is signalled by passing 1 as the io context to io_setup.
 */
#define REQUEST_ASYNC_FD ((io_context_t)1)

And if I create a basic test program, I can see that calling it with param 1 it does return EINVAL.

What is this patch the comment refers to? It was working under Debian 3.2.x

Thanks

James


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