Re: [PATCH v4 2/8] grep: skip pthreads overhead when using one thread
From: Ævar Arnfjörð Bjarmason <hidden>
Date: 2017-06-01 21:37:04
Subsystem:
the rest · Maintainer:
Linus Torvalds
On Thu, Jun 1, 2017 at 11:20 PM, Stefan Beller [off-list ref] wrote:
quoted hunk ↗ jump to hunk
On Thu, Jun 1, 2017 at 11:20 AM, Ævar Arnfjörð Bjarmason [off-list ref] wrote:quoted
+ if (num_threads == 1) + num_threads = 0;I would think that it is easier to maintain the code when keep the 1 hard coded, and apply the following diff instead. If we encounter a 0 later on, it is not clear what the original user input was. (Did the user ask for 0 as a proxy for GREP_NUM_THREADS_DEFAULT ? do they care about the number of threads?) It is less complexity in the decision logic here. --8<-- (white space broken)diff --git a/builtin/grep.c b/builtin/grep.c index c6c26e9b9e..6ad9b3da20 100644 --- a/builtin/grep.c +++ b/builtin/grep.c@@ -1231,7 +1231,7 @@ int cmd_grep(int argc, const char **argv, constchar *prefix) #endif #ifndef NO_PTHREADS - if (num_threads) { + if (num_threads > 1) { if (!(opt.name_only || opt.unmatch_name_only || opt.count) && (opt.pre_context || opt.post_context || opt.file_break || opt.funcbody))@@ -1295,7 +1295,7 @@ int cmd_grep(int argc, const char **argv, constchar *prefix) hit = grep_objects(&opt, &pathspec, &list); } - if (num_threads) + if (num_threads > 1) hit |= wait_all(); if (hit && show_in_pager) run_pager(&opt, prefix); --8<--
If I've understood you correctly (what I applied on top of this based on the above at the end of the mail) this segfaults because now we won't compile the pattern. I agree that this logic is a bit tricky, but it must be considered with the "!num_threads" logic in preceding "grep: don't redundantly compile throwaway patterns under threading" patch. I.e. we already have num_threads being assigned to 0 under NO_PTHREADS, doing the same for the PTHREADS codepath seemed like the simplest solution to me.
diff --git a/builtin/grep.c b/builtin/grep.c
index a0a3922f92..6d16df2526 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c@@ -1238,25 +1238,23 @@ int cmd_grep(int argc, const char **argv,const char *prefix)
num_threads = GREP_NUM_THREADS_DEFAULT;
else if (num_threads < 0)
die(_("invalid number of threads specified (%d)"), num_threads);
- if (num_threads == 1)
- num_threads = 0;
#else
if (num_threads)
warning(_("no threads support, ignoring --threads"));
- num_threads = 0;
+ num_threads = 0; /* If we have no threads... */
#endif
- if (!num_threads)
+ if (num_threads) /* Or if we've decided not to use them... */
/*
* The compiled patterns on the main path are only
* used when not using threading. Otherwise
* start_threads() below calls compile_grep_patterns()
* for each thread.
*/
- compile_grep_patterns(&opt);
+ compile_grep_patterns(&opt); /* We'll compile the
pattern here */
#ifndef NO_PTHREADS
- if (num_threads) {
+ if (num_threads > 1) {
if (!(opt.name_only || opt.unmatch_name_only || opt.count)
&& (opt.pre_context || opt.post_context ||
opt.file_break || opt.funcbody))@@ -1320,7 +1318,7 @@ int cmd_grep(int argc, const char **argv, constchar *prefix)
hit = grep_objects(&opt, &pathspec, &list);
}
- if (num_threads)
+ if (num_threads > 1)
hit |= wait_all();
if (hit && show_in_pager)
run_pager(&opt, prefix);