Hello,

I noticed a performace issue with emacs 25.1 (built with MinGW on
windows 10, but I used the one at
https://sourceforge.net/projects/emacsbinw64/).

I created a small c++ program to read from stdin:

std::cin >> fileSizeStr;
std::streamsize length = std::stoi(fileSizeStr);
char *content = (char *)malloc(length);
std::cin.read(content, length);

and sent data to it with the follogiwn emacs code :

;; added this in the middle of a 162 kb file and eval'd it:
(setq proc (start-process "Test" nil "./test.exe"))
(process-send-string
  proc
  (format "%d\n%s\n" (point-max)
  (buffer-substring (point-min) (point-max))))

I used elp-instrument-function for process-send-string and I got this
results (emacs 25.1 built by me vs emacs 24.5 found in msys2+mingw64
repo, compiled with the same flags):

* emacs 25.1: 0.510064 seconds/call
* emacs 24.5: 0.037496 seconds/call

And for a simple C program with fread(..., stdin) instead of std::cin

* emacs 25.1: 0.547136 seconds/call
* emacs 24.5: 0.031285 seconds/call


In GNU Emacs 25.1.1 (x86_64-w64-mingw32)
 of 2016-08-01 built on CSIRB-DEV
Windowing system distributor 'Microsoft Corp.', version 10.0.10586
Configured using:
 'configure --build=x86_64-w64-mingw32 --with-wide-int=yes
 --with-sound=yes --with-file-notification=yes --without-gpm
 --without-gconf --without-gsettings --without-selinux --with-modules
 'CFLAGS=-march=native -mtune=native -pipe -O3 -fomit-frame-pointer
 -funroll-loops' 'CPPFLAGS=-mtune=native -march=native -DNDEBUG -isystem
 /mingw64/include' 'LDFLAGS=-s -Wl,-s''

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND DBUS NOTIFY ACL GNUTLS LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS MODULES

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8

Major mode: C/l

Minor modes in effect:
  irony-mode: t
  delete-selection-mode: t
  global-auto-revert-mode: t
  recentf-mode: t
  savehist-mode: t
  save-place-mode: t
  show-paren-mode: t
  override-global-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  size-indication-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Mark saved where search started
#<process Test>
nil
Quit
#<process Test>
nil
Mark set
Quit
Reusing Dired buffers is now ON

Load-path shadows:
d:/tools/prog/home/csirb/.emacs.d/elpa/seq-2.16/seq hides d:/emacs/share/emacs/25.1/lisp/emacs-lisp/seq

Features:
(shadow sort mail-extr emacsbug message rfc822 mml mml-sec epg mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail rfc2047 rfc2045 ietf-drums mail-utils add-log dired+
image-dired image-file dired-x dired-aux dired elp colir color misearch
multi-isearch company-irony flycheck-irony irony-diagnostics
flycheck-tip error-tip notifications dbus xml popup flycheck rx subr-x
irony-cdb-libclang irony-cdb-json pp irony-cdb-clang-complete irony-cdb
irony-completion irony-snippet irony cc-mode cc-fonts cc-guess cc-menus
cc-cmds which-func imenu company-oddmuse company-keywords company-etags
company-gtags company-dabbrev-code company-dabbrev company-files
company-capf company-cmake company-xcode company-clang company-semantic
company-eclim company-template company-css company-nxml company-bbdb
company init init-keys init-prog init-python anaconda-mode pythonic f s
python tramp-sh json map url url-proxy url-privacy url-expand
url-methods url-history url-cookie url-domsuf url-util mailcap tramp
tramp-compat tramp-loaddefs trampver ucs-normalize shell init-lisp
init-c cc-styles cc-align cc-engine cc-vars cc-defs git-gutter
init-project projectile ibuf-ext ibuffer init-ido counsel jka-compr
esh-util swiper ivy ffap url-parse auth-source gnus-util mm-util
mail-prsvr password-cache url-vars smex ido init-dired init-editor
mouse-copy undo-tree diff wrap-region dash etags xref cl-seq project
eieio eieio-core cl-macs volatile-highlights tiny org org-macro
org-footnote org-pcomplete pcomplete org-list org-faces org-entities
noutline outline org-version ob-emacs-lisp ob ob-tangle ob-ref ob-lob
ob-table ob-exp org-src ob-keys ob-comint ob-core ob-eval org-compat
org-macs org-loaddefs format-spec find-func cal-menu calendar
cal-loaddefs help-fns which-key init-search iedit iedit-lib anzu
thingatpt grep compile comint ansi-color ring init-completion dabbrev
init-utils init-buffers edmacro kmacro init-advices advice init-sensible
delsel autorevert filenotify recentf tree-widget wid-edit savehist
saveplace init-appearance zenburn-theme paren use-package diminish
bind-key easy-mmode finder-inf info package epg-config seq byte-opt gv
bytecomp byte-compile cl-extra help-mode easymenu cconv cl-loaddefs
pcase cl-lib time-date mule-util tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel dos-w32 ls-lisp disp-table
w32-win w32-vars term/common-win tool-bar dnd fontset image regexp-opt
fringe tabulated-list newcomment elisp-mode lisp-mode prog-mode register
page menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock
font-lock syntax facemenu font-core frame cl-generic cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese charscript case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer cl-preloaded nadvice
loaddefs button faces cus-face macroexp files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote w32notify dbusbind w32 multi-tty
make-network-process emacs)

Memory information:
((conses 16 492637 123968)
 (symbols 56 45068 0)
 (miscs 48 157 220)
 (strings 32 107471 159315)
 (string-bytes 1 3362962)
 (vectors 16 64216)
 (vector-slots 8 990553 6398)
 (floats 8 572 95)
 (intervals 56 2108 72)
 (buffers 976 19)