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[Xen-devel] [PATCH v2 1/8] oxenstored: add a poll-based select mechanism

From: Zheng Li <dev@xxxxxxxx>

Date: Tue, 16 Sep 2014 10:31:30 +0100

Cc: Dave Scott <Dave.Scott@xxxxxxxxxx>, Joe Jin <joe.jin@xxxxxxxxxx>, "Luis R. Rodriguez" <mcgrof@xxxxxxxx>, Luonengjun <luonengjun@xxxxxxxxxx>, Zheng Li <dev@xxxxxxxx>, Fanhenglong <fanhenglong@xxxxxxxxxx>, "Liuqiming $John$" <john.liuqiming@xxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxx>

Delivery-date: Tue, 16 Sep 2014 17:06:48 +0000

List-id: Xen developer discussion <xen-devel.lists.xen.org>

Currently, oxenstored uses Unix.select underneath, so it doesn't work properly if given a FD number >= 1024. This is a scalability bottleneck for hosts running large number of VMs. To remove this limitation, we implemented a poll-based mechanism but with the same type signature as the Unix.select currently in use. So these two functions can be interchangeable at any stage. Signed-off-by: Zheng Li <dev@xxxxxxxx> --- tools/ocaml/xenstored/Makefile | 9 +++-- tools/ocaml/xenstored/select.ml | 54 ++++++++++++++++++++++++++++ tools/ocaml/xenstored/select.mli | 20 +++++++++++ tools/ocaml/xenstored/select_stubs.c | 68 ++++++++++++++++++++++++++++++++++++ tools/ocaml/xenstored/xenstored.ml | 2 +- 5 files changed, 149 insertions(+), 4 deletions(-) create mode 100644 tools/ocaml/xenstored/select.ml create mode 100644 tools/ocaml/xenstored/select.mli create mode 100644 tools/ocaml/xenstored/select_stubs.c diff --git a/tools/ocaml/xenstored/Makefile b/tools/ocaml/xenstored/Makefile index 068e04a..47d5303 100644 --- a/tools/ocaml/xenstored/Makefile +++ b/tools/ocaml/xenstored/Makefile @@ -15,10 +15,12 @@ OCAMLINCLUDE += \ -I $(OCAML_TOPLEVEL)/libs/xc \ -I $(OCAML_TOPLEVEL)/libs/eventchn -LIBS = syslog.cma syslog.cmxa +LIBS = syslog.cma syslog.cmxa select.cma select.cmxa syslog_OBJS = syslog syslog_C_OBJS = syslog_stubs -OCAML_LIBRARY = syslog +select_OBJS = select +select_C_OBJS = select_stubs +OCAML_LIBRARY = syslog select LIBS += systemd.cma systemd.cmxa systemd_OBJS = systemd @@ -46,12 +48,13 @@ OBJS = define \ process \ xenstored -INTF = symbol.cmi trie.cmi syslog.cmi systemd.cmi +INTF = symbol.cmi trie.cmi syslog.cmi systemd.cmi select.cmi XENSTOREDLIBS = \ unix.cmxa \ -ccopt -L -ccopt . syslog.cmxa \ -ccopt -L -ccopt . systemd.cmxa \ + -ccopt -L -ccopt . select.cmxa \ -ccopt -L -ccopt $(OCAML_TOPLEVEL)/libs/mmap $(OCAML_TOPLEVEL)/libs/mmap/xenmmap.cmxa \ -ccopt -L -ccopt $(OCAML_TOPLEVEL)/libs/eventchn $(OCAML_TOPLEVEL)/libs/eventchn/xeneventchn.cmxa \ -ccopt -L -ccopt $(OCAML_TOPLEVEL)/libs/xc $(OCAML_TOPLEVEL)/libs/xc/xenctrl.cmxa \ diff --git a/tools/ocaml/xenstored/select.ml b/tools/ocaml/xenstored/select.ml new file mode 100644 index 0000000..3f4b671 --- /dev/null +++ b/tools/ocaml/xenstored/select.ml @@ -0,0 +1,54 @@ +(* + * Copyright (C) 2014 Zheng Li <dev@xxxxxxxx> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU Lesser General Public License as published + * by the Free Software Foundation; version 2.1 only. with the special + * exception on linking described in file LICENSE. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU Lesser General Public License for more details. + *) + + +(* The [read], [write], [except] are fields mapped to the POLLIN/OUT/PRI + subscription flags used by poll, which have a correspondence to the + readfds, writefds, exceptfds concept as in select. *) +type event = { + mutable read: bool; + mutable write: bool; + mutable except: bool; +} + +external select_on_poll: (Unix.file_descr * event) array -> int -> int = "stub_select_on_poll" + +let init_event () = {read = false; write = false; except = false} + +let select in_fds out_fds exc_fds timeout = + let h = Hashtbl.create 57 in + let add_event event_set fd = + let e = + try Hashtbl.find h fd + with Not_found -> + let e = init_event () in + Hashtbl.add h fd e; e in + event_set e in + List.iter (add_event (fun x -> x.read <- true)) in_fds; + List.iter (add_event (fun x -> x.write <- true)) out_fds; + List.iter (add_event (fun x -> x.except <- true)) exc_fds; + (* Unix.stdin and init_event are dummy input as stubs, which will + always be overwritten later on. *) + let a = Array.make (Hashtbl.length h) (Unix.stdin, init_event ()) in + let i = ref (-1) in + Hashtbl.iter (fun fd event -> incr i; Array.set a !i (fd, event)) h; + let n = select_on_poll a (int_of_float (timeout *. 1000.)) in + let r = [], [], [] in + if n = 0 then r else + Array.fold_right + (fun (fd, event) (r, w, x) -> + (if event.read then fd :: r else r), + (if event.write then fd :: w else w), + (if event.except then fd :: x else x)) + a r diff --git a/tools/ocaml/xenstored/select.mli b/tools/ocaml/xenstored/select.mli new file mode 100644 index 0000000..1253d4e --- /dev/null +++ b/tools/ocaml/xenstored/select.mli @@ -0,0 +1,20 @@ +(* + * Copyright (C) 2014 Zheng Li <dev@xxxxxxxx> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU Lesser General Public License as published + * by the Free Software Foundation; version 2.1 only. with the special + * exception on linking described in file LICENSE. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU Lesser General Public License for more details. + *) + + +(** Same interface and semantics as [Unix.select] but with an extra alternative + implementation based on poll. *) +val select: + Unix.file_descr list -> Unix.file_descr list -> Unix.file_descr list -> float + -> Unix.file_descr list * Unix.file_descr list * Unix.file_descr list diff --git a/tools/ocaml/xenstored/select_stubs.c b/tools/ocaml/xenstored/select_stubs.c new file mode 100644 index 0000000..33beeb9 --- /dev/null +++ b/tools/ocaml/xenstored/select_stubs.c @@ -0,0 +1,68 @@ +/* + * Copyright (C) 2014 Zheng Li <dev@xxxxxxxx> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU Lesser General Public License as published + * by the Free Software Foundation; version 2.1 only. with the special + * exception on linking described in file LICENSE. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU Lesser General Public License for more details. + */ + +#include <poll.h> +#include <errno.h> +#include <sys/resource.h> +#include <unistd.h> +#include <caml/mlvalues.h> +#include <caml/memory.h> +#include <caml/fail.h> +#include <caml/alloc.h> +#include <caml/signals.h> +#include <caml/unixsupport.h> + +CAMLprim value stub_select_on_poll(value fd_events, value timeo) { + + CAMLparam2(fd_events, timeo); + CAMLlocal1(events); + int i, rc, c_len = Wosize_val(fd_events), c_timeo = Int_val(timeo); + struct pollfd c_fds[c_len]; + + + for (i = 0; i < c_len; i++) { + + events = Field(Field(fd_events, i), 1); + + c_fds[i].fd = Int_val(Field(Field(fd_events, i), 0)); + c_fds[i].events = c_fds[i].revents = 0; + c_fds[i].events |= Bool_val(Field(events, 0)) ? POLLIN : 0; + c_fds[i].events |= Bool_val(Field(events, 1)) ? POLLOUT: 0; + c_fds[i].events |= Bool_val(Field(events, 2)) ? POLLPRI: 0; + + }; + + caml_enter_blocking_section(); + rc = poll(c_fds, c_len, c_timeo); + caml_leave_blocking_section(); + + if (rc < 0) uerror("poll", Nothing); + + if (rc > 0) { + + for (i = 0; i < c_len; i++) { + + events = Field(Field(fd_events, i), 1); + + if (c_fds[i].revents & POLLNVAL) unix_error(EBADF, "select", Nothing); + Field(events, 0) = Val_bool(c_fds[i].events | POLLIN && c_fds[i].revents & (POLLIN |POLLHUP|POLLERR)); + Field(events, 1) = Val_bool(c_fds[i].events | POLLOUT && c_fds[i].revents & (POLLOUT|POLLHUP|POLLERR)); + Field(events, 2) = Val_bool(c_fds[i].revents & POLLPRI); + + } + + } + + CAMLreturn(Val_int(rc)); +} diff --git a/tools/ocaml/xenstored/xenstored.ml b/tools/ocaml/xenstored/xenstored.ml index 1c02f2f..bfa488f 100644 --- a/tools/ocaml/xenstored/xenstored.ml +++ b/tools/ocaml/xenstored/xenstored.ml @@ -368,7 +368,7 @@ let _ = let timeout = if List.length mw > 0 then 0. else -1. in let rset, wset, _ = try - Unix.select (spec_fds @ inset) outset [] timeout + Select.select (spec_fds @ inset) outset [] timeout with Unix.Unix_error(Unix.EINTR, _, _) -> [], [], [] in let sfds, cfds = -- 2.1.0 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel

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