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Date: Fri, 10 Feb 2012 09:03:42 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3 6/6] qemu_calculate_timeout: increase
 minimum timeout to 1h
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To: Paul Brook <paul@codesourcery.com>
Cc: avi@redhat.com, xen-devel@lists.xensource.com, qemu-devel@nongnu.org, Stefano Stabellini <stefano.stabellini@eu.citrix.com>

On 02/10/2012 01:26 AM, Paul Brook wrote:
> The reason we have this is because there are bits of code that rely on
> polling.  IIRC slirp and the floppy DMA engine were the main culprits.
> qemu_calculate_timeout is an ugly hack to poll at least once a second,
> allowing the guest to make forward progress when we miss an event.

At least the floppy DMA engine is fine with it, it uses idle bottom 
halves (which are a hack and could be replaced by timers, but that's not 
relevant now).

Slirp's timeouts indeed require polling.

                 if (time_fasttimo && ((curtime - time_fasttimo) >= 2)) {
                         tcp_fasttimo(slirp);
                         time_fasttimo = 0;
                 }
                 if (do_slowtimo && ((curtime - last_slowtimo) >= 499)) {
                         ip_slowtimo(slirp);
                         tcp_slowtimo(slirp);
                         last_slowtimo = curtime;
                 }

Paolo