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Diffstat (limited to 'tools/lib/python/jobserver.py')
| -rwxr-xr-x | tools/lib/python/jobserver.py | 195 |
1 files changed, 195 insertions, 0 deletions
diff --git a/tools/lib/python/jobserver.py b/tools/lib/python/jobserver.py new file mode 100755 index 000000000000..aba22c33393d --- /dev/null +++ b/tools/lib/python/jobserver.py @@ -0,0 +1,195 @@ +#!/usr/bin/env python3 +# SPDX-License-Identifier: GPL-2.0+ +# +# pylint: disable=C0103,C0209 +# +# + +""" +Interacts with the POSIX jobserver during the Kernel build time. + +A "normal" jobserver task, like the one initiated by a make subrocess would do: + + - open read/write file descriptors to communicate with the job server; + - ask for one slot by calling:: + + claim = os.read(reader, 1) + + - when the job finshes, call:: + + os.write(writer, b"+") # os.write(writer, claim) + +Here, the goal is different: This script aims to get the remaining number +of slots available, using all of them to run a command which handle tasks in +parallel. To to that, it has a loop that ends only after there are no +slots left. It then increments the number by one, in order to allow a +call equivalent to ``make -j$((claim+1))``, e.g. having a parent make creating +$claim child to do the actual work. + +The end goal here is to keep the total number of build tasks under the +limit established by the initial ``make -j$n_proc`` call. + +See: + https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver +""" + +import errno +import os +import subprocess +import sys + +def warn(text, *args): + print(f'WARNING: {text}', *args, file = sys.stderr) + +class JobserverExec: + """ + Claim all slots from make using POSIX Jobserver. + + The main methods here are: + + - open(): reserves all slots; + - close(): method returns all used slots back to make; + - run(): executes a command setting PARALLELISM=<available slots jobs + 1>. + """ + + def __init__(self): + """Initialize internal vars.""" + self.claim = 0 + self.jobs = b"" + self.reader = None + self.writer = None + self.is_open = False + + def open(self): + """Reserve all available slots to be claimed later on.""" + + if self.is_open: + return + self.is_open = True # We only try once + self.claim = None + # + # Check the make flags for "--jobserver=R,W" + # Note that GNU Make has used --jobserver-fds and --jobserver-auth + # so this handles all of them. + # + flags = os.environ.get('MAKEFLAGS', '') + opts = [x for x in flags.split(" ") if x.startswith("--jobserver")] + if not opts: + return + # + # Separate out the provided file descriptors + # + split_opt = opts[-1].split('=', 1) + if len(split_opt) != 2: + warn('unparseable option:', opts[-1]) + return + fds = split_opt[1] + # + # As of GNU Make 4.4, we'll be looking for a named pipe + # identified as fifo:path + # + if fds.startswith('fifo:'): + path = fds[len('fifo:'):] + try: + self.reader = os.open(path, os.O_RDONLY | os.O_NONBLOCK) + self.writer = os.open(path, os.O_WRONLY) + except (OSError, IOError): + warn('unable to open jobserver pipe', path) + return + # + # Otherwise look for integer file-descriptor numbers. + # + else: + split_fds = fds.split(',') + if len(split_fds) != 2: + warn('malformed jobserver file descriptors:', fds) + return + try: + self.reader = int(split_fds[0]) + self.writer = int(split_fds[1]) + except ValueError: + warn('non-integer jobserver file-descriptors:', fds) + return + try: + # + # Open a private copy of reader to avoid setting nonblocking + # on an unexpecting process with the same reader fd. + # + self.reader = os.open(f"/proc/self/fd/{self.reader}", + os.O_RDONLY | os.O_NONBLOCK) + except (IOError, OSError) as e: + warn('Unable to reopen jobserver read-side pipe:', repr(e)) + return + # + # OK, we have the channel to the job server; read out as many jobserver + # slots as possible. + # + while True: + try: + slot = os.read(self.reader, 8) + if not slot: + # + # Something went wrong. Clear self.jobs to avoid writing + # weirdness back to the jobserver and give up. + self.jobs = b"" + warn("unexpected empty token from jobserver;" + " possible invalid '--jobserver-auth=' setting") + self.claim = None + return + except (OSError, IOError) as e: + # + # If there is nothing more to read then we are done. + # + if e.errno == errno.EWOULDBLOCK: + break + # + # Anything else says that something went weird; give back + # the jobs and give up. + # + if self.jobs: + os.write(self.writer, self.jobs) + self.claim = None + warn('error reading from jobserver pipe', repr(e)) + return + self.jobs += slot + # + # Add a bump for our caller's reserveration, since we're just going + # to sit here blocked on our child. + # + self.claim = len(self.jobs) + 1 + + def close(self): + """Return all reserved slots to Jobserver.""" + + if not self.is_open: + return + + # Return all the reserved slots. + if len(self.jobs): + os.write(self.writer, self.jobs) + + self.is_open = False + + def __enter__(self): + self.open() + return self + + def __exit__(self, exc_type, exc_value, exc_traceback): + self.close() + + def run(self, cmd, *args, **pwargs): + """ + Run a command setting PARALLELISM env variable to the number of + available job slots (claim) + 1, e.g. it will reserve claim slots + to do the actual build work, plus one to monitor its children. + """ + self.open() # Ensure that self.claim is set + + # We can only claim parallelism if there was a jobserver (i.e. a + # top-level "-jN" argument) and there were no other failures. Otherwise + # leave out the environment variable and let the child figure out what + # is best. + if self.claim: + os.environ["PARALLELISM"] = str(self.claim) + + return subprocess.call(cmd, *args, **pwargs) |