Andrew Geissler | 7e0e3c0 | 2022-02-25 20:34:39 +0000 | [diff] [blame^] | 1 | Upstream-Status: Backport |
| 2 | Signed-off-by: Ross Burton <ross.burton@arm.com> |
| 3 | |
| 4 | PR28804: tune default stap -s ## buffer size on small RAM machines |
| 5 | |
| 6 | Insert a forgotten division by num_online_cpu() to adjust downward the |
| 7 | calculated bufsize. Tweak normal defaults back to 128 * 2 * 64K |
| 8 | (16MB) per CPU, as the stap man page indicates. This may need further |
| 9 | tweaking when balancing against staprun consumption performance, but |
| 10 | at least we have the docs lined up with the code at the moment. |
| 11 | |
| 12 | PR28804: tune default stap -s ## buffer size on small RAM machines |
| 13 | |
| 14 | Use si_meminfo to limit default buffer size. Note in the man page |
| 15 | that the "-s ##" parameter is per-CPU. |
| 16 | |
| 17 | diff --git a/man/stap.1.in b/man/stap.1.in |
| 18 | index 55dbc2c93..285a27b34 100644 |
| 19 | --- a/man/stap.1.in |
| 20 | +++ b/man/stap.1.in |
| 21 | @@ -239,8 +239,8 @@ and average amount of time spent in each probe-point. Also shows |
| 22 | the derivation for each probe-point. |
| 23 | .TP |
| 24 | .BI \-s " NUM" |
| 25 | -Use NUM megabyte buffers for kernel-to-user data transfer. On a |
| 26 | -multiprocessor in bulk mode, this is a per-processor amount. |
| 27 | +Use NUM megabyte buffers for kernel-to-user data transfer per processor. |
| 28 | +The default is 16MB, or less on smaller memory machines. |
| 29 | .TP |
| 30 | .BI \-I " DIR" |
| 31 | Add the given directory to the tapset search directory. See the |
| 32 | diff --git a/runtime/transport/transport.c b/runtime/transport/transport.c |
| 33 | index 18ecccea2..44afff814 100644 |
| 34 | --- a/runtime/transport/transport.c |
| 35 | +++ b/runtime/transport/transport.c |
| 36 | @@ -72,8 +72,11 @@ static inline void _stp_unlock_inode(struct inode *inode); |
| 37 | #include "procfs.c" |
| 38 | #include "control.c" |
| 39 | |
| 40 | -static unsigned _stp_nsubbufs = 256; |
| 41 | -static unsigned _stp_subbuf_size = 8 * STP_BUFFER_SIZE; /* 64K */ |
| 42 | +/* set default buffer parameters. User may override these via stap -s #, and |
| 43 | + the runtime may auto-shrink it on low memory machines too. */ |
| 44 | +/* NB: Note default in man/stap.1.in */ |
| 45 | +static unsigned _stp_nsubbufs = 128; |
| 46 | +static unsigned _stp_subbuf_size = 2 * STP_BUFFER_SIZE; /* 2 * 64K */ |
| 47 | |
| 48 | /* module parameters */ |
| 49 | static int _stp_bufsize; |
| 50 | @@ -602,17 +605,30 @@ static int _stp_transport_init(void) |
| 51 | _stp_need_kallsyms_stext = 0; |
| 52 | #endif |
| 53 | |
| 54 | - if (_stp_bufsize) { |
| 55 | - unsigned size = _stp_bufsize * 1024 * 1024; |
| 56 | + if (_stp_bufsize == 0) { // option not specified? |
| 57 | + struct sysinfo si; |
| 58 | + long _stp_bufsize_avail; |
| 59 | + si_meminfo(&si); |
| 60 | + _stp_bufsize_avail = (long)((si.freeram + si.bufferram) / 4 / num_online_cpus()) |
| 61 | + << PAGE_SHIFT; // limit to quarter of free ram total |
| 62 | + if ((_stp_nsubbufs * _stp_subbuf_size * num_online_cpus()) > _stp_bufsize_avail) { |
| 63 | + _stp_bufsize = max_t (int, 1, _stp_bufsize_avail / 1024 / 1024); |
| 64 | + dbug_trans(1, "Shrinking default _stp_bufsize to %d MB/cpu due to low free memory\n", _stp_bufsize); |
| 65 | + } |
| 66 | + } |
| 67 | + |
| 68 | + if (_stp_bufsize) { // overridden by user or by si_meminfo heuristic? |
| 69 | + long size = _stp_bufsize * 1024 * 1024; |
| 70 | _stp_subbuf_size = 65536; |
| 71 | + // bump up subbuf size from 64K to 1M to keep _stp_nsubbufs not too large |
| 72 | while (size / _stp_subbuf_size > 64 && |
| 73 | _stp_subbuf_size < 1024 * 1024) { |
| 74 | _stp_subbuf_size <<= 1; |
| 75 | } |
| 76 | _stp_nsubbufs = size / _stp_subbuf_size; |
| 77 | - dbug_trans(1, "Using %d subbufs of size %d\n", _stp_nsubbufs, _stp_subbuf_size); |
| 78 | } |
| 79 | - |
| 80 | + dbug_trans(1, "Using %d subbufs of size %d\n", _stp_nsubbufs, _stp_subbuf_size); |
| 81 | + |
| 82 | ret = _stp_transport_fs_init(THIS_MODULE->name); |
| 83 | if (ret) |
| 84 | goto err0; |