small fixes to the perf script (#78)

motivation: keep script up to date

changes:
* use 5.3 nightly
* better support for perf symlink as the location is a moving target
* info about cold/warm start

Author: tomerd

scripts/linux_performance_setup.sh

@@ -13,7 +13,7 @@
 ##
 ##===----------------------------------------------------------------------===##
 
-# docker run --privileged -it -v `pwd`:/code -w /code swiftlang/swift:nightly-5.2-bionic bash
+# docker run --privileged -it -v `pwd`:/code -w /code swiftlang/swift:nightly-5.3-bionic bash
 
 apt-get update -y
 apt-get install -y vim htop strace linux-tools-common linux-tools-generic libc6-dbg
@@ -22,7 +22,7 @@ echo 0 > /proc/sys/kernel/kptr_restrict
 
 cd /usr/bin
 rm -rf perf
-ln -s /usr/lib/linux-tools/4.15.0-91-generic/perf perf
+ln -s /usr/lib/linux-tools/*/perf perf
 cd -
 
 cd /opt
@@ -36,11 +36,11 @@ cd -
 # (.build/release/MockServer) &
 #
 # strace
-# export MAX_REQUESTS=10000
+# export MAX_REQUESTS=10000 (or MAX_REQUESTS=1 for cold start analysis)
 # strace -o .build/strace-c-string-$MAX_REQUESTS -c .build/release/StringSample
 # strace -o .build/strace-ffftt-string-$MAX_REQUESTS -fftt .build/release/StringSample
 #
 # perf
-# export MAX_REQUESTS=10000
+# export MAX_REQUESTS=10000 (or MAX_REQUESTS=1 for cold start analysis)
 # perf record -o .build/perf-$MAX_REQUESTS.data -g -F 100000 .build/release/StringSample dwarf
 # perf script -i .build/perf-$MAX_REQUESTS.data | /opt/FlameGraph/stackcollapse-perf.pl | swift-demangle | /opt/FlameGraph/flamegraph.pl > .build/flamegraph-$MAX_REQUESTS.svg