| Message ID | 1431021095-7558-2-git-send-email-jsnow@redhat.com |
|---|---|
| State | New |
| Headers | show |
On 05/07/2015 11:51 AM, John Snow wrote: > Instead of converting each byte one-at-a-time and then sending each byte > over the wire, use sprintf() to pre-compute all of the hex nibs into a > single buffer, then send the entire buffer all at once. > > This gives a moderate speed boost to memread() and memwrite() functions. > > Signed-off-by: John Snow <jsnow@redhat.com> > --- > - qtest_send_prefix(chr); > - qtest_send(chr, "OK 0x"); > + enc = g_malloc(2 * len + 1); > for (i = 0; i < len; i++) { > - qtest_sendf(chr, "%02x", data[i]); > + sprintf(&enc[i * 2], "%02x", data[i]); Making a function call to sprintf() has a lot of overhead. Isn't it even faster to open-code the conversion, something like: for (i = 0; i < len; i++) { const char digits[] = "0123456789abcdef"; enc[i * 2] = digits[data[i] >> 4]; enc[i * 2 + 1] = digits[data[i] & 0xf]; } enc[len * 2] = '\0';
On 05/07/2015 04:21 PM, Eric Blake wrote: > On 05/07/2015 11:51 AM, John Snow wrote: >> Instead of converting each byte one-at-a-time and then sending >> each byte over the wire, use sprintf() to pre-compute all of the >> hex nibs into a single buffer, then send the entire buffer all at >> once. >> >> This gives a moderate speed boost to memread() and memwrite() >> functions. >> >> Signed-off-by: John Snow <jsnow@redhat.com> --- > >> - qtest_send_prefix(chr); - qtest_send(chr, "OK >> 0x"); + enc = g_malloc(2 * len + 1); for (i = 0; i < len; >> i++) { - qtest_sendf(chr, "%02x", data[i]); + >> sprintf(&enc[i * 2], "%02x", data[i]); > > Making a function call to sprintf() has a lot of overhead. Isn't > it even faster to open-code the conversion, something like: > "Maybe." > for (i = 0; i < len; i++) { const char digits[] = > "0123456789abcdef"; enc[i * 2] = digits[data[i] >> 4]; enc[i * 2 + > 1] = digits[data[i] & 0xf]; } enc[len * 2] = '\0'; > In practice I didn't see a statistical difference between my previous nib-encoding function on my machine and this sprintf version, so I opted not to add any new bit twiddling. The bulk of the savings comes from not engaging the full socket send for two bytes over and over and over again. --js
John Snow <jsnow@redhat.com> writes: > Instead of converting each byte one-at-a-time and then sending each byte > over the wire, use sprintf() to pre-compute all of the hex nibs into a > single buffer, then send the entire buffer all at once. > > This gives a moderate speed boost to memread() and memwrite() functions. > > Signed-off-by: John Snow <jsnow@redhat.com> Reviewed-by: Markus Armbruster <armbru@redhat.com>
diff --git a/qtest.c b/qtest.c index c4999c3..d4e931f 100644 --- a/qtest.c +++ b/qtest.c @@ -414,6 +414,7 @@ static void qtest_process_command(CharDriverState *chr, gchar **words) } else if (strcmp(words[0], "read") == 0) { uint64_t addr, len, i; uint8_t *data; + char *enc; g_assert(words[1] && words[2]); addr = strtoull(words[1], NULL, 0); @@ -422,14 +423,16 @@ static void qtest_process_command(CharDriverState *chr, gchar **words) data = g_malloc(len); cpu_physical_memory_read(addr, data, len); - qtest_send_prefix(chr); - qtest_send(chr, "OK 0x"); + enc = g_malloc(2 * len + 1); for (i = 0; i < len; i++) { - qtest_sendf(chr, "%02x", data[i]); + sprintf(&enc[i * 2], "%02x", data[i]); } - qtest_send(chr, "\n"); + + qtest_send_prefix(chr); + qtest_sendf(chr, "OK 0x%s\n", enc); g_free(data); + g_free(enc); } else if (strcmp(words[0], "b64read") == 0) { uint64_t addr, len; uint8_t *data; diff --git a/tests/libqtest.c b/tests/libqtest.c index 055aad6..e5188e0 100644 --- a/tests/libqtest.c +++ b/tests/libqtest.c @@ -730,13 +730,15 @@ void qtest_memwrite(QTestState *s, uint64_t addr, const void *data, size_t size) { const uint8_t *ptr = data; size_t i; + char *enc = g_malloc(2 * size + 1); - qtest_sendf(s, "write 0x%" PRIx64 " 0x%zx 0x", addr, size); for (i = 0; i < size; i++) { - qtest_sendf(s, "%02x", ptr[i]); + sprintf(&enc[i * 2], "%02x", ptr[i]); } - qtest_sendf(s, "\n"); + + qtest_sendf(s, "write 0x%" PRIx64 " 0x%zx 0x%s\n", addr, size, enc); qtest_rsp(s, 0); + g_free(enc); } void qtest_memset(QTestState *s, uint64_t addr, uint8_t pattern, size_t size)
Instead of converting each byte one-at-a-time and then sending each byte over the wire, use sprintf() to pre-compute all of the hex nibs into a single buffer, then send the entire buffer all at once. This gives a moderate speed boost to memread() and memwrite() functions. Signed-off-by: John Snow <jsnow@redhat.com> --- qtest.c | 11 +++++++---- tests/libqtest.c | 8 +++++--- 2 files changed, 12 insertions(+), 7 deletions(-)