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Date: Fri, 30 Mar 2012 20:37:29 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] slirp: Signal free input buffer space to
	io-thread
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To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: qemu-devel <qemu-devel@nongnu.org>

Il 30/03/2012 19:43, Jan Kiszka ha scritto:
> This massively accelerates slirp reception speed: If data arrives
> faster than the guest can read it from the input buffer, the file
> descriptor for the corresponding socket was taken out of the fdset for
> select. However, the event of the guest reading enough data from the
> buffer was not signaled. Thus, the io-thread only noticed this change
> on the next time-driven poll. Fix this by kicking the io-thread as
> required.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
> 
> Hell, this was really annoying when working with slirp, specifically
> with KVM irqchip enabled (as it reduces userspace exits). But I never
> really found the time to dig deep enough. And now it turned out to be
> so simple! http://thread.gmane.org/gmane.comp.emulators.qemu/141975 was
> the key for me.
> 
>  slirp/sbuf.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/slirp/sbuf.c b/slirp/sbuf.c
> index 5a1ccbf..637f8fe 100644
> --- a/slirp/sbuf.c
> +++ b/slirp/sbuf.c
> @@ -6,6 +6,7 @@
>   */
>  
>  #include <slirp.h>
> +#include <main-loop.h>
>  
>  static void sbappendsb(struct sbuf *sb, struct mbuf *m);
>  
> @@ -18,6 +19,8 @@ sbfree(struct sbuf *sb)
>  void
>  sbdrop(struct sbuf *sb, int num)
>  {
> +    int limit = sb->sb_datalen / 2;
> +
>  	/*
>  	 * We can only drop how much we have
>  	 * This should never succeed
> @@ -29,6 +32,9 @@ sbdrop(struct sbuf *sb, int num)
>  	if(sb->sb_rptr >= sb->sb_data + sb->sb_datalen)
>  		sb->sb_rptr -= sb->sb_datalen;
>  
> +    if (sb->sb_cc < limit && sb->sb_cc + num >= limit) {
> +        qemu_notify_event();
> +    }
>  }
>  
>  void

Looks good!

Paolo