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s390/debug: only write data once

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debug_event_common memsets the active debug entry with zeros to
prevent stale data leakage. This is overwritten with the actual
debug data in the next step. Only write zeros to that part of the
debug entry that's not used by new debug data.

Micro benchmarks show a 2-10% reduction of cpu cycles with this
approach.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Acked-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Sebastian Ott 2017-10-12 13:57:26 +02:00 committed by Martin Schwidefsky
parent 94158e544f
commit 0dcd91a9e6
1 changed files with 4 additions and 2 deletions
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6
arch/s390/kernel/debug.c
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@ -902,8 +902,9 @@ debug_entry_t *debug_event_common(debug_info_t *id, int level, const void *buf,
}
do {
active = get_active_entry(id);
memset(DEBUG_DATA(active), 0, id->buf_size);
memcpy(DEBUG_DATA(active), buf, min(len, id->buf_size));
if (len < id->buf_size)
memset((DEBUG_DATA(active)) + len, 0, id->buf_size - len);
debug_finish_entry(id, active, level, 0);
len -= id->buf_size;
buf += id->buf_size;
@ -934,8 +935,9 @@ debug_entry_t *debug_exception_common(debug_info_t *id, int level,
}
do {
active = get_active_entry(id);
memset(DEBUG_DATA(active), 0, id->buf_size);
memcpy(DEBUG_DATA(active), buf, min(len, id->buf_size));
if (len < id->buf_size)
memset((DEBUG_DATA(active)) + len, 0, id->buf_size - len);
debug_finish_entry(id, active, level, len <= id->buf_size);
len -= id->buf_size;
buf += id->buf_size;