From: Sergey Bugaev <bugaevc@gmail.com>
To: libc-alpha@sourceware.org, bug-hurd@gnu.org
Cc: Samuel Thibault <samuel.thibault@gnu.org>,
Sergey Bugaev <bugaevc@gmail.com>
Subject: [PATCH 1/1] hurd: Avoid extra ctty RPCs in init_dtable ()
Date: Sat, 15 Apr 2023 19:17:18 +0300 [thread overview]
Message-ID: <20230415161718.80668-2-bugaevc@gmail.com> (raw)
In-Reply-To: <20230415161718.80668-1-bugaevc@gmail.com>
It is common to have (some of) stdin, stdout and stderr point to the
very same port. We were making the ctty RPCs that _hurd_port2fd () does
for each one of them separately:
1. term_getctty ()
2. mach_port_deallocate ()
3. term_open_ctty ()
Instead, let's detect this case and duplicate the ctty port we already
have. This means we do 1 RPC instead of 3 (and create a single protid
on the server side) if the file is our ctty, and no RPCs instead of 1
if it's not. A clear win!
Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
---
hurd/dtable.c | 46 +++++++++++++++++++++++++++++++++++++++-------
1 file changed, 39 insertions(+), 7 deletions(-)
diff --git a/hurd/dtable.c b/hurd/dtable.c
index 5dd04131..41f4d7af 100644
--- a/hurd/dtable.c
+++ b/hurd/dtable.c
@@ -60,18 +60,50 @@ init_dtable (void)
_hurd_dtable[i] = NULL;
else
{
+ int copy;
/* Allocate a new file descriptor structure. */
struct hurd_fd *new = malloc (sizeof (struct hurd_fd));
if (new == NULL)
__libc_fatal ("hurd: Can't allocate initial file descriptors\n");
- /* Initialize the port cells. */
- _hurd_port_init (&new->port, MACH_PORT_NULL);
- _hurd_port_init (&new->ctty, MACH_PORT_NULL);
-
- /* Install the port in the descriptor.
- This sets up all the ctty magic. */
- _hurd_port2fd (new, _hurd_init_dtable[i], 0);
+ /* See if this file descriptor is the same as a previous one we have
+ already installed. In this case, we can just copy over the same
+ ctty port without making any more RPCs. We only check the the
+ immediately preceding fd and fd 0 -- this should be enough to
+ handle the common cases while not requiring quadratic
+ complexity. */
+ if (i > 0 && _hurd_init_dtable[i] == _hurd_init_dtable[i - 1])
+ copy = i - 1;
+ else if (i > 0 && _hurd_init_dtable[i] == _hurd_init_dtable[0])
+ copy = 0;
+ else
+ copy = -1;
+
+ if (copy < 0)
+ {
+ /* Initialize the port cells. */
+ _hurd_port_init (&new->port, MACH_PORT_NULL);
+ _hurd_port_init (&new->ctty, MACH_PORT_NULL);
+
+ /* Install the port in the descriptor.
+ This sets up all the ctty magic. */
+ _hurd_port2fd (new, _hurd_init_dtable[i], 0);
+ }
+ else
+ {
+ /* Copy over ctty from the already set up file descriptor that
+ contains the same port. We can access the contents of the
+ cell without any locking since no one could have seen it
+ yet. */
+ mach_port_t ctty = _hurd_dtable[copy]->ctty.port;
+
+ if (MACH_PORT_VALID (ctty))
+ __mach_port_mod_refs (__mach_task_self (), ctty,
+ MACH_PORT_RIGHT_SEND, +1);
+
+ _hurd_port_init (&new->port, _hurd_init_dtable[i]);
+ _hurd_port_init (&new->ctty, ctty);
+ }
_hurd_dtable[i] = new;
}
--
2.39.2
next prev parent reply other threads:[~2023-04-15 16:17 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-15 16:17 [PATCH 0/1] Let's improve/fix ccty handling Sergey Bugaev
2023-04-15 16:17 ` Sergey Bugaev [this message]
2023-04-17 12:08 ` [PATCH 1/1] hurd: Avoid extra ctty RPCs in init_dtable () Samuel Thibault
2023-04-15 17:58 ` [PATCH 0/1] Let's improve/fix ccty handling Samuel Thibault
2023-04-15 19:08 ` [PATCH] hurd: Run init_pids () before init_dtable () Sergey Bugaev
2023-04-17 21:05 ` Samuel Thibault
2023-04-17 12:14 ` [PATCH 0/1] Let's improve/fix ccty handling Samuel Thibault
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