Date: Thu, 19 Dec 2013 11:59:06 -0800 From: Adrian Chadd <adrian@freebsd.org> To: Gleb Smirnoff <glebius@freebsd.org> Cc: Jack F Vogel <jfv@freebsd.org>, Michael Tuexen <Michael.Tuexen@lurchi.franken.de>, Ryan Stone <rysto32@gmail.com>, freebsd-net <freebsd-net@freebsd.org> Subject: Re: Removing queue length check in ip_output (was Re: buf_ring in HEAD is racy) Message-ID: <CAJ-VmonYRb9jQKbXLuurQrrjaUzQcwiRze0O7g2A5s=KPBjDKw@mail.gmail.com> In-Reply-To: <CAJ-Vmo=jCo-H8BwybFS3uaS3xQ4pxSz-hpxyEg0z2g3KSoErwQ@mail.gmail.com> References: <CAJ-VmomyPq_2K-MFhb7vt6MM7RBbmn7yaTzUXb7%2BN7TbW1RmHQ@mail.gmail.com> <20131219151606.GB71033@FreeBSD.org> <CAJ-Vmo=jCo-H8BwybFS3uaS3xQ4pxSz-hpxyEg0z2g3KSoErwQ@mail.gmail.com>
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How's this?
Index: sys/netinet/ip_output.c
===================================================================
--- sys/netinet/ip_output.c (revision 259474)
+++ sys/netinet/ip_output.c (working copy)
@@ -123,7 +123,9 @@
struct mbuf *m0;
int hlen = sizeof (struct ip);
int mtu;
+#if 0
int n; /* scratchpad */
+#endif
int error = 0;
struct sockaddr_in *dst;
const struct sockaddr_in *gw;
@@ -431,6 +433,25 @@
}
/*
+ * Both in the SMP world, pre-emption world if_transmit() world,
+ * the following code doesn't really function as intended any further.
+ *
+ * + There can and will be multiple CPUs running this code path
+ * in parallel, and we do no lock holding when checking the
+ * queue depth;
+ * + And since other threads can be running concurrently, even if
+ * we do pass this check, another thread may queue some frames
+ * before this thread does and it will end up partially or fully
+ * failing to send anyway;
+ * + if_transmit() based drivers don't necessarily set ifq_len
+ * at all.
+ *
+ * This should be replaced with a method of pushing an entire list
+ * of fragment frames to the driver and have the driver decide
+ * whether it can queue or not queue the entire set.
+ */
+#if 0
+ /*
* Verify that we have any chance at all of being able to queue the
* packet or packet fragments, unless ALTQ is enabled on the given
* interface in which case packetdrop should be done by queueing.
@@ -446,6 +467,7 @@
ifp->if_snd.ifq_drops += n;
goto bad;
}
+#endif
/*
* Look for broadcast address and
-a
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