s390/debug: only write data once (0dcd91a9) · Commits · 戴 / test

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>

arch/s390/kernel/debug.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -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;

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