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In our codebase, `cond_resched() and `schedule()` are Linux kernel
functions that have replaced the OpenSolaris `kpreempt()` functions in
the codebase to such an extent that `kpreempt()` in zfs_context.h was
broken. Nobody noticed because we did not actually use it. The header
had defined `kpreempt()` as `yield()`, which works on OpenSolaris and
Illumos where `sched_yield()` is a wrapper for `yield()`, but that does
not work on any other platform.
The FreeBSD platform specific code implemented shims for these, but the
shim for `schedule()` forced us to wait, which is different than merely
rescheduling to another thread as the original Linux code does, while
the shim for `cond_resched()` had the same definition as its kernel
kpreempt() shim.
After studying this, I have concluded that we should reintroduce the
kpreempt() function in platform independent code with the following
definitions:
- In the Linux kernel:
kpreempt(unused) -> cond_resched()
- In the FreeBSD kernel:
kpreempt(unused) -> kern_yield(PRI_USER)
- In userspace:
kpreempt(unused) -> sched_yield()
In userspace, nothing changes from this cleanup. In the kernels, the
function `fm_fini()` will now call `kern_yield(PRI_USER)` on FreeBSD and
`cond_resched()` on Linux. This is instead of `pause("schedule", 1)` on
FreeBSD and `schedule()` on Linux. This makes our behavior consistent
across platforms.
Note that Linux's SPL continues to use `cond_resched()` and
`schedule()`. However, those functions have been removed from both the
FreeBSD code and userspace code.
This should have the benefit of making it slightly easier to port the
code to new platforms by making how things should be mapped less
confusing.
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Neal Gompa <ngompa@datto.com>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #13845
39 lines
1.5 KiB
C
39 lines
1.5 KiB
C
/*
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* Copyright (c) 2013 Andriy Gapon
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* $FreeBSD$
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*/
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#ifndef _OPENSOLARIS_SYS_DISP_H_
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#define _OPENSOLARIS_SYS_DISP_H_
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#include <sys/proc.h>
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#define KPREEMPT_SYNC (-1)
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#define kpreempt(x) kern_yield(PRI_USER)
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#endif /* _OPENSOLARIS_SYS_DISP_H_ */
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