[Xen-ia64-devel] Re: [Xen-devel] Re: [PATCH 0/3][IA64] Accelerate IDE PIO on HVM/IA64

[Kouya SHIMURA <kouya@xxxxxxxxxxxxxx>]

Hi Alex,

Thanks for pointing out bugs. I'll check the whole code again.

For domain shutting down, my patch does nothing.  But the original
qemu (or real IDE controller chip also?) is involved in the same
problem. The dirty data will be missing by sudden death of a guest. 
A guest OS has the responsibility to flush the dirty buffer.

I might have to consider save/restore of hvm. That is a future work.

Thanks,
Kouya

Alex Williamson writes:
 > On Tue, 2007-02-27 at 18:34 +0900, Kouya SHIMURA wrote:
 > > Hi,
 > > 
 > > This set of patches remarkably accelerates IDE PIO on HVM/IA64.
 > > I got a throughput of 2.11MB/sec in disk read performance.
 > > Without it, it was only 64kB/sec.
 > > 
 > > I posted the prototype once. 
 > > http://lists.xensource.com/archives/html/xen-devel/2006-12/msg00077.html
 > > 
 > > The basic idea is to add a buffering mechanism in a hypervisor.
 > > I know this approach is not sophisticated. But there is no other
 > > good way in IA64 which has no string instructions like x86's.
 > 
 >    This seems like a pretty good performance increase for only a single
 > page of domain overhead in Xen.  My main concern would be that we
 > maintain correctness.  It is writing out the dirty buffer before the
 > domain shuts down, right?  I'm guessing the flush probably does that.
 > Looks like a bug here though:
 > 
 > +static inline void
 > +buffered_pio_write(IDEState *s, uint32_t addr, int size)
 > +{
 > +    struct pio_buffer *piobuf = piobuf_by_addr(addr);
 > +    uint32_t data_end;
 > +
 > +    if (!piobuf)
 > +        return;
 > +    buffered_pio_flush(piobuf);
 > +    data_end = s->data_end - s->data_ptr - size;
 > +    if (data_end <= 0)
 > +        data_end = 0;
 > 
 >    data_end is unsigned, so it will never be < 0.  Same problem on the
 > read func.  Thanks,
 > 
 >      Alex
 > 
 > -- 
 > Alex Williamson                             HP Open Source & Linux Org.
 > 
 > 
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 > Xen-devel@xxxxxxxxxxxxxxxxxxx
 > http://lists.xensource.com/xen-devel


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