From: Dmitry Safonov <dima@arista.com>
To: linux-kernel@vger.kernel.org
Cc: Dmitry Safonov <0x7f454c46@gmail.com>,
Dmitry Safonov <dima@arista.com>, Adrian Reber <adrian@lisas.de>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andrei Vagin <avagin@openvz.org>,
Andy Lutomirski <luto@kernel.org>,
Cyrill Gorcunov <gorcunov@openvz.org>,
Ingo Molnar <mingo@redhat.com>, Oleg Nesterov <oleg@redhat.com>,
Pavel Emelyanov <xemul@virtuozzo.com>,
Thomas Gleixner <tglx@linutronix.de>,
containers@lists.linux-foundation.org,
linux-fsdevel@vger.kernel.org
Subject: [PATCH 3/9] select: Convert __esimate_accuracy() to ktime_t
Date: Mon, 9 Sep 2019 11:23:34 +0100 [thread overview]
Message-ID: <20190909102340.8592-4-dima@arista.com> (raw)
In-Reply-To: <20190909102340.8592-1-dima@arista.com>
__estimate_accuracy() divides 64-bit integers twice which is suboptimal.
Converting to ktime_t not only avoids that, but also simplifies the
logic on some extent.
The long-term goal is to convert poll() to leave timeout value in
ktime_t inside restart_block as it's the only user that leaves it in
timespec. That's a preparation ground for introducing a new ptrace()
request that will dump timeout for interrupted syscall.
Furthermore, do_select() and do_poll() actually both need time in
ktime_t for poll_schedule_timeout(), so there is this hack that converts
time on the first loop. It's not only a "hack", but also it's done every
time poll() syscall is restarted. After conversion it'll be removed.
While at it, rename parameters "slack" and "timeout" which describe
their purpose better.
Signed-off-by: Dmitry Safonov <dima@arista.com>
---
fs/select.c | 33 +++++++++++++--------------------
1 file changed, 13 insertions(+), 20 deletions(-)
diff --git a/fs/select.c b/fs/select.c
index 53a0c149f528..12cdefd3be2d 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -36,7 +36,7 @@
/*
- * Estimate expected accuracy in ns from a timeval.
+ * Estimate expected accuracy in ns.
*
* After quite a bit of churning around, we've settled on
* a simple thing of taking 0.1% of the timeout as the
@@ -49,22 +49,17 @@
#define MAX_SLACK (100 * NSEC_PER_MSEC)
-static long __estimate_accuracy(struct timespec64 *tv)
+static long __estimate_accuracy(ktime_t slack)
{
- long slack;
int divfactor = 1000;
- if (tv->tv_sec < 0)
+ if (slack < 0)
return 0;
if (task_nice(current) > 0)
divfactor = divfactor / 5;
- if (tv->tv_sec > MAX_SLACK / (NSEC_PER_SEC/divfactor))
- return MAX_SLACK;
-
- slack = tv->tv_nsec / divfactor;
- slack += tv->tv_sec * (NSEC_PER_SEC/divfactor);
+ slack = ktime_divns(slack, divfactor);
if (slack > MAX_SLACK)
return MAX_SLACK;
@@ -72,27 +67,25 @@ static long __estimate_accuracy(struct timespec64 *tv)
return slack;
}
-u64 select_estimate_accuracy(struct timespec64 *tv)
+u64 select_estimate_accuracy(struct timespec64 *timeout)
{
- u64 ret;
- struct timespec64 now;
+ ktime_t now, slack;
/*
* Realtime tasks get a slack of 0 for obvious reasons.
*/
-
if (rt_task(current))
return 0;
- ktime_get_ts64(&now);
- now = timespec64_sub(*tv, now);
- ret = __estimate_accuracy(&now);
- if (ret < current->timer_slack_ns)
- return current->timer_slack_ns;
- return ret;
-}
+ now = ktime_get();
+ slack = now - timespec64_to_ktime(*timeout);
+ slack = __estimate_accuracy(slack);
+ if (slack < current->timer_slack_ns)
+ return current->timer_slack_ns;
+ return slack;
+}
struct poll_table_page {
struct poll_table_page * next;
--
2.23.0
next prev parent reply other threads:[~2019-09-09 10:24 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-09 10:23 [PATCH 0/9] restart_block: Prepare the ground for dumping timeout Dmitry Safonov
2019-09-09 10:23 ` [PATCH 1/9] futex: Remove unused uaddr2 in restart_block Dmitry Safonov
2019-09-09 10:23 ` [PATCH 2/9] restart_block: Prevent userspace set part of the block Dmitry Safonov
2019-09-09 10:23 ` Dmitry Safonov [this message]
2019-09-09 10:23 ` [PATCH 4/9] select: Micro-optimise __estimate_accuracy() Dmitry Safonov
2019-09-09 11:18 ` Cyrill Gorcunov
2019-09-09 11:50 ` Dmitry Safonov
2019-09-09 12:14 ` Cyrill Gorcunov
2019-09-19 14:05 ` Cyrill Gorcunov
2019-09-19 14:25 ` Dmitry Safonov
2019-09-09 10:23 ` [PATCH 5/9] select: Convert select_estimate_accuracy() to take ktime_t Dmitry Safonov
2019-09-09 10:23 ` [PATCH 6/9] select: Extract common code into do_sys_ppoll() Dmitry Safonov
2019-09-09 11:15 ` kbuild test robot
2019-09-09 19:48 ` kbuild test robot
2019-09-09 10:23 ` [PATCH 7/9] select: Use ktime_t in do_sys_poll() and do_poll() Dmitry Safonov
2019-09-09 10:23 ` [PATCH 8/9] select/restart_block: Convert poll's timeout to u64 Dmitry Safonov
2019-09-09 13:07 ` David Laight
2019-09-16 15:19 ` Dmitry Safonov
2019-09-09 10:23 ` [PATCH 9/9] restart_block: Make common timeout Dmitry Safonov
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