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Message-ID: <1288386348.2680.25.camel@edumazet-laptop>
Date: Fri, 29 Oct 2010 23:05:48 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: Davide Libenzi <davidel@...ilserver.org>
Cc: Alban Crequy <alban.crequy@...labora.co.uk>,
"David S. Miller" <davem@...emloft.net>,
Stephen Hemminger <shemminger@...tta.com>,
Cyrill Gorcunov <gorcunov@...nvz.org>,
Alexey Dobriyan <adobriyan@...il.com>, netdev@...r.kernel.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Pauli Nieminen <pauli.nieminen@...labora.co.uk>,
Rainer Weikusat <rweikusat@...gmbh.com>
Subject: Re: [PATCH 0/1] RFC: poll/select performance on datagram sockets
Following patch solves the problem for me, and its only a start, I am
pretty sure we can optimize more than that.
What I did is to move "struct poll_wqueues table;" out of do_select()
in its caller. This structure is highly modified by an other cpu in
Alban workload, and this slow down do_select() because many accesses to
some of its local variables (normally, private ones !) hit a false
sharing.
Before :
# time /root/uclient connected
The performance problem will be triggered
select: begin
select: end: 3 seconds
real 0m3.101s
user 0m0.000s
sys 0m6.104s
After :
# time /root/uclient connected
The performance problem will be triggered
select: begin
select: end: 1 seconds
real 0m1.041s
user 0m0.004s
sys 0m2.040s
Impressive no ?
Reported-by: Alban Crequy <alban.crequy@...labora.co.uk>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
fs/compat.c | 3 ++-
fs/select.c | 19 ++++++++++---------
include/linux/poll.h | 3 ++-
3 files changed, 14 insertions(+), 11 deletions(-)
diff --git a/fs/compat.c b/fs/compat.c
index ff66c0d..3c3c3d3 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1704,6 +1704,7 @@ int compat_core_sys_select(int n, compat_ulong_t __user *inp,
int size, max_fds, ret = -EINVAL;
struct fdtable *fdt;
long stack_fds[SELECT_STACK_ALLOC/sizeof(long)];
+ struct poll_wqueues table;
if (n < 0)
goto out_nofds;
@@ -1744,7 +1745,7 @@ int compat_core_sys_select(int n, compat_ulong_t __user *inp,
zero_fd_set(n, fds.res_out);
zero_fd_set(n, fds.res_ex);
- ret = do_select(n, &fds, end_time);
+ ret = do_select(n, &fds, end_time, &table);
if (ret < 0)
goto out;
diff --git a/fs/select.c b/fs/select.c
index b7b10aa..ed054f5 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -393,10 +393,10 @@ static inline void wait_key_set(poll_table *wait, unsigned long in,
}
}
-int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
+int do_select(int n, fd_set_bits *fds, struct timespec *end_time,
+ struct poll_wqueues *table)
{
ktime_t expire, *to = NULL;
- struct poll_wqueues table;
poll_table *wait;
int retval, i, timed_out = 0;
unsigned long slack = 0;
@@ -409,8 +409,8 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
return retval;
n = retval;
- poll_initwait(&table);
- wait = &table.pt;
+ poll_initwait(table);
+ wait = &table->pt;
if (end_time && !end_time->tv_sec && !end_time->tv_nsec) {
wait = NULL;
timed_out = 1;
@@ -482,8 +482,8 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
wait = NULL;
if (retval || timed_out || signal_pending(current))
break;
- if (table.error) {
- retval = table.error;
+ if (table->error) {
+ retval = table->error;
break;
}
@@ -497,12 +497,12 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
to = &expire;
}
- if (!poll_schedule_timeout(&table, TASK_INTERRUPTIBLE,
+ if (!poll_schedule_timeout(table, TASK_INTERRUPTIBLE,
to, slack))
timed_out = 1;
}
- poll_freewait(&table);
+ poll_freewait(table);
return retval;
}
@@ -528,6 +528,7 @@ int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
struct fdtable *fdt;
/* Allocate small arguments on the stack to save memory and be faster */
long stack_fds[SELECT_STACK_ALLOC/sizeof(long)];
+ struct poll_wqueues table;
ret = -EINVAL;
if (n < 0)
@@ -570,7 +571,7 @@ int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
zero_fd_set(n, fds.res_out);
zero_fd_set(n, fds.res_ex);
- ret = do_select(n, &fds, end_time);
+ ret = do_select(n, &fds, end_time, &table);
if (ret < 0)
goto out;
diff --git a/include/linux/poll.h b/include/linux/poll.h
index 56e76af..54ba625 100644
--- a/include/linux/poll.h
+++ b/include/linux/poll.h
@@ -130,7 +130,8 @@ void zero_fd_set(unsigned long nr, unsigned long *fdset)
#define MAX_INT64_SECONDS (((s64)(~((u64)0)>>1)/HZ)-1)
-extern int do_select(int n, fd_set_bits *fds, struct timespec *end_time);
+extern int do_select(int n, fd_set_bits *fds, struct timespec *end_time,
+ struct poll_wqueues *table);
extern int do_sys_poll(struct pollfd __user * ufds, unsigned int nfds,
struct timespec *end_time);
extern int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
--
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