Re: [Xen-devel][RFC]degradation on IPF due to hypercall set irq

[Keir Fraser <keir@xxxxxxxxxxxxx>]

On 24/11/06 07:08, "Xu, Anthony" <anthony.xu@xxxxxxxxx> wrote:

> This patch is for comments, and it is based on IPF, it may not apply to IA32
> side.
> 
> This patch delivers interrupt and IO finish in the same hypercall
> xc_hvm_set_irq_and_wakeup_cpu,
> This eliminate all unnecessary hypercalls.
> In the meantime, I add a mechanism for IDE DMA thread to wakeup qemu main
> block(select) to
> Deliver IDE DMA interrupt.

Firstly, this patch is not against unstable tip.

Secondly, we should make multicalls work rather than kludge a
set_irq_and_notify_io_done type of hypercall. Applications are free to
include any of the Xen public headers. We really just need a xc_multicall()
API function.

Thirdly, either we should keep the independent IDE-DMA thread or it should
be entirely incorporated into the main qemu thread. Are pipe writes much
faster than just doing a hypercall? If much slower, why is that? Could you
work out a way of generically making IPC hypercalls faster (particularly
from privileged user space -- could you trap straight to the hypervisor from
user space rather than bouncing through guest kernel?).

 -- Keir


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