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Subject[PATCH 3/9] select: Convert __esimate_accuracy() to ktime_t
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__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
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