New sendfile(2) syscall. A joint effort of NGINX and Netflix from 2013 and

up to now.

The new sendfile is the code that Netflix uses to send their multiple tens
of gigabits of data per second. The new implementation features asynchronous
I/O, when I/O operations are launched, but not awaited to be complete. An
explanation of why such behavior is beneficial compared to old one is
going to be too long for a commit message, so we will skip it here.

Additional features of new syscall are extra flags, which provide an
application more control over data sent. The SF_NOCACHE flag tells
kernel that data shouldn't be cached after it was sent. The SF_READAHEAD()
macro allows to specify readahead size in pages.

The new syscalls is a drop in replacement. No modifications are required
to applications. One can take nginx binary for stable/10 and run it
successfully on head. Although SF_NODISKIO lost its original sense, as now
sendfile doesn't block, and now means something completely different (tm),
using the new sendfile the old way is absolutely safe.

Celebrates:	Netflix global launch!
Sponsored by:	Nginx, Inc.
Sponsored by:	Netflix
Relnotes:	yes

1 files changed, 23 insertions, 3 deletions

diff --git a/usr.bin/netstat/mbuf.c b/usr.bin/netstat/mbuf.c
index baf7a65..8b95ddd 100644
--- a/usr.bin/netstat/mbuf.c
+++ b/usr.bin/netstat/mbuf.c
@@ -326,13 +326,33 @@ mbpr(void *kvmd, u_long mbaddr)
 	    kread_counters) != 0)
 		goto out;
 
+        xo_emit("{:sendfile-syscalls/%ju} {N:sendfile syscalls}\n",
+	    (uintmax_t)sfstat.sf_syscalls); 
+        xo_emit("{:sendfile-no-io/%ju} "
+	    "{N:sendfile syscalls completed without I\\/O request}\n", 
+            (uintmax_t)sfstat.sf_noiocnt);
+	xo_emit("{:sendfile-io-count/%ju} "
+	    "{N:requests for I\\/O initiated by sendfile}\n",
+	    (uintmax_t)sfstat.sf_iocnt);
+        xo_emit("{:sendfile-pages-sent/%ju} "
+	    "{N:pages read by sendfile as part of a request}\n",
+            (uintmax_t)sfstat.sf_pages_read);
+        xo_emit("{:sendfile-pages-valid/%ju} "
+	    "{N:pages were valid at time of a sendfile request}\n",
+            (uintmax_t)sfstat.sf_pages_valid);
+        xo_emit("{:sendfile-requested-readahead/%ju} "
+	    "{N:pages were requested for read ahead by applications}\n",
+            (uintmax_t)sfstat.sf_rhpages_requested);
+        xo_emit("{:sendfile-readahead/%ju} "
+	    "{N:pages were read ahead by sendfile}\n",
+            (uintmax_t)sfstat.sf_rhpages_read);
+	xo_emit("{:sendfile-busy-encounters/%ju} "
+	    "{N:times sendfile encountered an already busy page}\n",
+	    (uintmax_t)sfstat.sf_busy);
 	xo_emit("{:sfbufs-alloc-failed/%ju} {N:requests for sfbufs denied}\n",
 	    (uintmax_t)sfstat.sf_allocfail);
 	xo_emit("{:sfbufs-alloc-wait/%ju} {N:requests for sfbufs delayed}\n",
 	    (uintmax_t)sfstat.sf_allocwait);
-	xo_emit("{:sfbufs-io-count/%ju} "
-	    "{N:requests for I\\/O initiated by sendfile}\n",
-	    (uintmax_t)sfstat.sf_iocnt);
 out:
 	xo_close_container("mbuf-statistics");
 	memstat_mtl_free(mtlp);