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bhyve: stability and performance improvement for dbgport

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The TCP server implementation in dbgport does not track clients, so it
may try to write to a disconected socket resulting in SIGPIPE.
Avoid that by setting SO_NOSIGPIPE socket option.

Because dbgport emulates an I/O port to guest, the communication is done
byte by byte.  Reduce latency of the TCP/IP transfers by using
TCP_NODELAY option.  In my tests that change improves performance of
kgdb commands with lots of output (e.g. info threads) by two orders of
magnitude.

A general note.  Since we have a uart emulation in bhyve, that can be
used for the console and gdb access to guests.  So, bvmconsole and bvmdebug
could be de-orbited now.  But there are many existing deployments that
still dependend on those.

Discussed with:	julian, jhb
MFC after:	2 weeks
Sponsored by:	Panzura
This commit is contained in:
Andriy Gapon 2016-11-29 13:11:00 +00:00
parent 605a51e323
commit 9aaefb2c53
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=309295
1 changed files with 12 additions and 2 deletions
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14
usr.sbin/bhyve/dbgport.c
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@ -32,6 +32,7 @@ __FBSDID("$FreeBSD$");
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <sys/uio.h>
#include <stdio.h>
@ -55,8 +56,9 @@ static int
dbg_handler(struct vmctx *ctx, int vcpu, int in, int port, int bytes,
uint32_t *eax, void *arg)
{
char ch;
int nwritten, nread, printonce;
int on = 1;
char ch;
if (bytes == 2 && in) {
*eax = BVM_DBG_SIG;
@ -74,8 +76,16 @@ dbg_handler(struct vmctx *ctx, int vcpu, int in, int port, int bytes,
printonce = 1;
}
conn_fd = accept4(listen_fd, NULL, NULL, SOCK_NONBLOCK);
if (conn_fd < 0 && errno != EINTR)
if (conn_fd >= 0) {
/* Avoid EPIPE after the client drops off. */
(void)setsockopt(conn_fd, SOL_SOCKET, SO_NOSIGPIPE,
&on, sizeof(on));
/* Improve latency for one byte at a time tranfers. */
(void)setsockopt(conn_fd, IPPROTO_TCP, TCP_NODELAY,
&on, sizeof(on));
} else if (errno != EINTR) {
perror("accept");
}
}
if (in) {