Skip to content

Reduce number of syscalls in rand - #53725

Merged
bors merged 3 commits into
rust-lang:masterfrom
tbu-:pr_getrandom_syscalls
Sep 2, 2018
Merged

Reduce number of syscalls in rand#53725
bors merged 3 commits into
rust-lang:masterfrom
tbu-:pr_getrandom_syscalls

Conversation

@tbu-

@tbu-tbu- commented Aug 26, 2018•
edited
Loading

Copy link
Copy Markdown
Contributor

This skips the initial zero-length getrandom call and
directly hands the user buffer to the operating system, saving one
getrandom syscall.

@tbu-
Reduce number of syscalls in rand
09a615c
In case that it is statically known that the OS doesn't support
`getrandom` (non-Linux) or becomes clear at runtime that `getrandom`
isn't available (`ENOSYS`), the opened fd ("/dev/urandom") isn't closed
after the function, so that future calls can reuse it. This saves
repeated `open`/`close` system calls at the cost of one permanently open
fd.
Additionally, this skips the initial zero-length `getrandom` call and
directly hands the user buffer to the operating system, saving one
`getrandom` syscall.
@rust-highfive

rust-highfive commented Aug 26, 2018

Copy link
Copy Markdown
Contributor

r? @Mark-Simulacrum

(rust_highfive has picked a reviewer for you, use r? to override)

@rust-highfiverust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 26, 2018
@Mark-Simulacrum

Mark-Simulacrum commented Aug 26, 2018

Copy link
Copy Markdown
Member

r? @alexcrichton

@tbu-

tbu- commented Aug 27, 2018

Copy link
Copy Markdown
ContributorAuthor

Program:

use std::collections::HashMap;
fn main() {
let mut m = HashMap::new();
m.insert("abc", "def");
}

Without this PR:

[…]
sigaltstack(NULL, {ss_sp=NULL, ss_flags=SS_DISABLE, ss_size=0}) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f072df95000
sigaltstack({ss_sp=0x7f072df95000, ss_flags=0, ss_size=8192}, NULL) = 0
getrandom("", 0, GRND_NONBLOCK) = 0
getrandom("\x26\x53\x69\xb8\x75\xd4\xe3\x9a\x32\x11\x10\x58\xa7\x8a\x47\x4b", 16, GRND_NONBLOCK) = 16
sigaltstack({ss_sp=NULL, ss_flags=SS_DISABLE, ss_size=8192}, NULL) = 0
munmap(0x7f072df95000, 8192) = 0
exit_group(0) = ?
+++ exited with 0 +++

With this PR:

[…]
sigaltstack(NULL, {ss_sp=NULL, ss_flags=SS_DISABLE, ss_size=0}) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa8d3862000
sigaltstack({ss_sp=0x7fa8d3862000, ss_flags=0, ss_size=8192}, NULL) = 0
getrandom("\x05\x08\x66\x91\x2a\xf0\x05\xf9\x44\x34\x7c\x27\xf3\xfe\x06\x4c", 16, GRND_NONBLOCK) = 16
sigaltstack({ss_sp=NULL, ss_flags=SS_DISABLE, ss_size=8192}, NULL) = 0
munmap(0x7fa8d3862000, 8192) = 0
exit_group(0) = ?
+++ exited with 0 +++

The initial getrandom("", 0, GRND_NONBLOCK) = 0 gets skipped.

@alexcrichton

alexcrichton commented Aug 27, 2018

Copy link
Copy Markdown
Member

Thanks for the PR! The changes to getrandom seem good to me, but I'm not super comfortable with effectively leaking a permanent file descriptor. This isn't really a performance sensitive piece of code, right? (It's only used sparingly on each thread I think?) In that sense is it really necessary to get the minor boost from leaving it open rather than closing and reopening?

@tbu-

tbu- commented Aug 29, 2018

Copy link
Copy Markdown
ContributorAuthor

Done.

@alexcrichton

alexcrichton commented Aug 29, 2018

Copy link
Copy Markdown
Member

@bors: r+

@bors

bors commented Aug 29, 2018

Copy link
Copy Markdown
Collaborator

📌 Commit 6d47737 has been approved by alexcrichton

@borsbors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 29, 2018
emilyalbini added a commit to emilyalbini/rust that referenced this pull request Aug 29, 2018
@emilyalbini
Rollup merge ofrust-lang#53725- tbu-:pr_getrandom_syscalls, r=alexc…
b18ecbd
…richton
Reduce number of syscalls in `rand`
This skips the initial zero-length `getrandom` call and
directly hands the user buffer to the operating system, saving one
`getrandom` syscall.
@emilyalbiniemilyalbini mentioned this pull request Aug 29, 2018
Closed
@emilyalbini

emilyalbini commented Aug 29, 2018

Copy link
Copy Markdown
Member

@bors r-

[00:25:39] error: unused import: `libc`
[00:25:39] --> libstd/sys/unix/rand.rs:32:9
[00:25:39] |
[00:25:39] 32 | use libc;
[00:25:39] | ^^^^
[00:25:39] |
[00:25:39] = note: `-D unused-imports` implied by `-D warnings`
[00:25:39] [00:25:39] error: unused import: `sys::os::errno`
[00:25:39] --> libstd/sys/unix/rand.rs:33:9
[00:25:39] |
[00:25:39] 33 | use sys::os::errno;
[00:25:39] | ^^^^^^^^^^^^^^
[00:25:39] [00:25:43] error: aborting due to 2 previous errors

@borsbors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Aug 29, 2018
@tbu-
tbu-force-pushed the pr_getrandom_syscalls branch from 6d47737 to d6d280bCompareAugust 29, 2018 20:30
goffrie
goffrie reviewed Aug 31, 2018
View reviewed changes
Comment threadsrc/libstd/sys/unix/rand.rs
if err == libc::EINTR {
continue;
} else if err == libc::ENOSYS {
GETRANDOM_UNAVAILABLE.store(true, Ordering::Relaxed);

@goffriegoffrieAug 31, 2018

Copy link
Copy Markdown
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Would this not loop infinitely in the ENOSYS case?

@tbu-tbu-Sep 1, 2018

Copy link
Copy Markdown
ContributorAuthor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Oh my...

@alexcrichton

alexcrichton commented Aug 31, 2018

Copy link
Copy Markdown
Member

@bors: r-

oh dear, good eyes @goffrie!

@alexcrichton

alexcrichton commented Sep 2, 2018

Copy link
Copy Markdown
Member

@bors: r+

@bors

bors commented Sep 2, 2018

Copy link
Copy Markdown
Collaborator

📌 Commit b95c491 has been approved by alexcrichton

@borsbors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Sep 2, 2018
@bors

bors commented Sep 2, 2018

Copy link
Copy Markdown
Collaborator

⌛ Testing commit b95c491 with merge 9395f0a...

bors added a commit that referenced this pull request Sep 2, 2018
@bors
Auto merge of#53725- tbu-:pr_getrandom_syscalls, r=alexcrichton
9395f0a
Reduce number of syscalls in `rand`
This skips the initial zero-length `getrandom` call and
directly hands the user buffer to the operating system, saving one
`getrandom` syscall.
@bors

bors commented Sep 2, 2018

Copy link
Copy Markdown
Collaborator

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing 9395f0a to master...

@bors
bors merged commit b95c491 into rust-lang:masterSep 2, 2018
@tbu-tbu- mentioned this pull request Mar 6, 2024
Merged
Sign up for freeto join this conversation on GitHub. Already have an account? Sign in to comment

Reviewers

1 more reviewer
@goffriegoffriegoffrie left review comments
Reviewers whose approvals may not affect merge requirements

Assignees

@alexcrichtonalexcrichton

Labels

S-waiting-on-borsStatus: Waiting on bors to run and complete tests. Bors will change the label on completion.

Projects

None yet

Milestone

No milestone

Development

Successfully merging this pull request may close these issues.

7 participants

@tbu-@rust-highfive@Mark-Simulacrum@alexcrichton@bors@emilyalbini@goffrie