/* * Copyright (C) 2010, 2015 Mathieu Desnoyers * * membarrier system call * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * 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 General Public License for more details. */ #include #include /* * Bitmask made from a "or" of all commands within enum membarrier_cmd, * except MEMBARRIER_CMD_QUERY. */ #define MEMBARRIER_CMD_BITMASK (MEMBARRIER_CMD_SHARED) /** * sys_membarrier - issue memory barriers on a set of threads * @cmd: Takes command values defined in enum membarrier_cmd. * @flags: Currently needs to be 0. For future extensions. * * If this system call is not implemented, -ENOSYS is returned. If the * command specified does not exist, or if the command argument is invalid, * this system call returns -EINVAL. For a given command, with flags argument * set to 0, this system call is guaranteed to always return the same value * until reboot. * * All memory accesses performed in program order from each targeted thread * is guaranteed to be ordered with respect to sys_membarrier(). If we use * the semantic "barrier()" to represent a compiler barrier forcing memory * accesses to be performed in program order across the barrier, and * smp_mb() to represent explicit memory barriers forcing full memory * ordering across the barrier, we have the following ordering table for * each pair of barrier(), sys_membarrier() and smp_mb(): * * The pair ordering is detailed as (O: ordered, X: not ordered): * * barrier() smp_mb() sys_membarrier() * barrier() X X O * smp_mb() X O O * sys_membarrier() O O O */ SYSCALL_DEFINE2(membarrier, int, cmd, int, flags) { if (unlikely(flags)) return -EINVAL; switch (cmd) { case MEMBARRIER_CMD_QUERY: return MEMBARRIER_CMD_BITMASK; case MEMBARRIER_CMD_SHARED: if (num_online_cpus() > 1) synchronize_sched(); return 0; default: return -EINVAL; } } /cgit.cgi/linux/net-next.git/log/tools/perf/Documentation/perf-top.txt'>
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authorDexuan Cui <decui@microsoft.com>2017-01-28 11:46:02 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-01-31 10:59:48 +0100
commit433e19cf33d34bb6751c874a9c00980552fe508c (patch)
treece6547ef2987fbb289fa28f03536328a42781651 /tools/perf/Documentation/perf-top.txt
parent191e885a2e130e639bb0c8ee350d7047294f2ce6 (diff)
Drivers: hv: vmbus: finally fix hv_need_to_signal_on_read()
Commit a389fcfd2cb5 ("Drivers: hv: vmbus: Fix signaling logic in hv_need_to_signal_on_read()") added the proper mb(), but removed the test "prev_write_sz < pending_sz" when making the signal decision. As a result, the guest can signal the host unnecessarily, and then the host can throttle the guest because the host thinks the guest is buggy or malicious; finally the user running stress test can perceive intermittent freeze of the guest. This patch brings back the test, and properly handles the in-place consumption APIs used by NetVSC (see get_next_pkt_raw(), put_pkt_raw() and commit_rd_index()). Fixes: a389fcfd2cb5 ("Drivers: hv: vmbus: Fix signaling logic in hv_need_to_signal_on_read()") Signed-off-by: Dexuan Cui <decui@microsoft.com> Reported-by: Rolf Neugebauer <rolf.neugebauer@docker.com> Tested-by: Rolf Neugebauer <rolf.neugebauer@docker.com> Cc: "K. Y. Srinivasan" <kys@microsoft.com> Cc: Haiyang Zhang <haiyangz@microsoft.com> Cc: Stephen Hemminger <sthemmin@microsoft.com> Cc: <stable@vger.kernel.org> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'tools/perf/Documentation/perf-top.txt')