I am new to perf_event_open(), and I have several questions;
So I am trying to collect addresses of pages that triggers MEM_LOAD_RETIRED.L3_MISS and MEM_INST_RETIRED.ALL_STORES for mysqld under sampled mode.
Under sample mode, I am using mmap to read from a ring buffer, I know that
The first page should be perf_event_mmap_page, followed by 2^n pages as the ring buffer.
My question is, in the data section[the blue section], is the mmap values arranged in a way like
a) perf_event_header followed by data, followed by data, followed by perf_event_header, followed by data
b) perf_event_header followed by data, followed by data, followed by data
I am assuming the mmap values are arranged by a), and I find that I constantly collect address 0x0 when setting
attr.type = PERF_TYPE_HARDWARE;
attr.config = PERF_COUNT_HW_INSTRUCTIONS;
P.S. I have read through this post, Using perf_event_open() to get sample address ,however the addr=0, and I am very sure that I am testing on a physical machine.
and collect nothing at all when using the following configurations:
type = PERF_TYPE_HARDWARE
config = PERF_COUNT_HW_CACHE_MISSES | PERF_COUNT_HW_CACHE_REFERENCES
type = PERF_TYPE_HW_CACHE
config = PERF_COUNT_HW_CACHE_LL | (PERF_COUNT_HW_CACHE_OP_READ << 8) | (PERF_COUNT_HW_CACHE_RESULT_MISS << 16)
And also, what are the differences between the above two configurations? they seem both to be collecting hardware caches.
I also find that I can collect info when
monitoring current process[pid = 0],
and some processes[for example pid = 1],
but not for the others, for example, mysqld
Many thanks in advance! Help of any kind is welcomed!
Related
In trying to implement some card emulation using NFCPY, I've come across the NDEF data type. I've attached its records along with their comment explanations below.
ndef_data_area = bytearray(64 * 16)
ndef_data_area[0] = 0x10 # NDEF mapping version '1.0'
ndef_data_area[1] = 12 # Number of blocks that may be read at once
ndef_data_area[2] = 8 # Number of blocks that may be written at once
ndef_data_area[4] = 63 # Number of blocks available for NDEF data
ndef_data_area[10] = 1 # NDEF read and write operations are allowed
ndef_data_area[14:16] = struct.pack('>H', sum(ndef_data_area[0:14])) # Checksum
My question is, how can I manually encode a file into these records (NDEF fields)?
I've come across mobile apps that enable the transmission of GPS data, emails, text messages, but I am unsure of how these programs interact with the records of the NDEF data type as they are shown above. As a weaker problem, I tried encoding a string into the NDEF fields, but I am told that only integers are accepted.
So some docs on the Ndef standards are available to read at https://github.com/haldean/ndef/tree/master/docs
Some types of data can be handled by "Well Known" types, some types can be handled as "URI" type, e.g. //, email://
A lot of more custom stuff is handled by Mime Type records e.g. "image/png", "application/vcard", etc
I am working on a project,in which I need to extract data from the device: InertialUnit.
I get a single value in real time, but I need data for the first 10 s and in 1 ms increments, or all the data for the entire cycle of the device. Please help me implement this if possible.
Webots controllers are like any other programs, so you can easily get the values of the inertial unit and save them in a file at each step.
Here is a very simple example in Python:
from controller import Robot
robot = Robot()
inertial_unit = robot.getInertialUnit('inertial unit')
inertial_unit.enable(10)
while robot.step(10) != -1:
values = inertial_unit.getValues()
with open('values.txt','a') as f:
f.write('\n'.join(values))
I am writing a software which processes audio files. I am using libsndfile library for reading wave file data, and I come across a doubt that wasn't solved by their documentation: what is the difference between functions that read items and functions that read frames? Or, in other words, am I getting the same results if I interchange both sf_read_short and sf_readf_short?
I have read in some questions that an audio frame equals a single sample, so I thought that what libsndfile calls items might be the same thing. During my tests they seemed to be the same.
I was concerned too and found the answer.
Q12 : I'm looking at sf_read*. What are items? What are frames?
An item is a single sample of the data type you are reading; ie a
single short value for sf_read_short or a single float for
sf_read_float. For a sound file with only one channel, a frame is the
same as a item (ie a single sample) while for multi channel sound
files, a single frame contains a single item for each channel.
Here are two simple, correct examples, both of which are assumed to be
working on a stereo file, first using items:
#define CHANNELS 2
short data [CHANNELS * 100] ;
sf_count items_read = sf_read_short (file, data, 200) ;
assert (items_read == 200) ;
and now readng the exact same amount of data using frames:
#define CHANNELS 2
short data [CHANNELS * 100] ;
sf_count frames_read = sf_readf_short (file, data, 100) ;
assert (frames_read == 100) ;
This is a copy&paste from:
libsndfile FAQ, question 12.
Currently I am sending the UART the strings I want to log and reading it on the host with any terminal.
In order to reduce the logging time and hopefully the image size as well (my flash is tiny), I figured out that the strings are unused in the embedded system, so why storing them on the flash?
I want to implement a server, whom I can send a hashed-key of any string (for example - it's ROM address) and the string will be output to file or screen.
My questions are:
How to create the key2string converter out of the image file (the OS is CMX, but can be answered generally)
Is there a recomended way to generate image, that will know the strings addresses but will exclude them from ROM?
Is there a known generic (open-source or other) that implemented a similar logger?
Thanks
Rather than holding hard-coded strings, then trying to hash the answers and sent it via a UART, then somehow remove the strings from the resulting image, I suggest the following.
Just send an index for an error code. The PC side can look up that index and determine what the string is for that condition. If you want the device code to be more clear, the index can be an enumeration.
For example:
enum errorStrings
{
ES_valueOutOfLimits = 1,
ES_wowItsGettingWarm = 2,
ES_randomError = 3,
ES_passwordFailure = 4
};
So, if you were sending data to the UART via printf, you could do the following:
printf("%d\n",(int)ES_wowItsGettingWarm);
Then your PC software just needs to decode the "2" that comes across the UART back into a useful string of "Wow it's getting warm."
This keeps the firmware small, but you need to manually keep the file containing the enum and the file with the strings in sync.
My solution is sending file name and line (which should be 14-20 Byte) and having a source parser on the server side, which will generate map of the actual texts. This way the actual code will contain no "format" strings, but single "filename" string for each file. Furthermore, file names can be easily replaced with enum (unlike replacing every string in the code) to reduce the COMM throughput.
I hope the sample psaudo-code will help clarifying the idea:
/* target code */
#define PRINT(format,...) send(__FILE__,__LINE__,__VA_ARGS__)
...
/* host code (c++) */
void PrintComm(istream& in)
{
string fileName;
int line,nParams;
int* params;
in>>fileName>>line>>nParams;
if (nParams>0)
{
params = new int[nParams];
for (int i=0; i<nParams; ++i)
in>>params[i];
}
const char* format = FindFormat(fileName,line);
...
delete[] params;
}
We are making a device and it has 8 serial ports. It runs on the Monta Vista Pro5 kernel. And we are working in C.
Suppose: A device gets attached to ttyUSB0, ttyUSB1 and ttyUSB2. The next device gets connected to ttyUSB3 and another to ttyUSB4. How can I know which device gets attached to which port ?? ie ttyUSB0 or ttyUSB1 or so on. Is there a way to directly query the device and find which port it is attached to. Or, in C, open ttyUSB0, query it somehow and get some reply as to which device it is ??
A rather complicated way: do a stat of, say /dev/ttyUSB0. Get the device number. And search for this in /proc/bus/usb/devices and find the vendor id or something to identify the device.
Or: Is there some way to reserve ttyUSB0,ttyUSB1 and ttyUSB2 for one device, ttyUSB3 for another and so on when they are plugged in ? This way I will know which device is connected to which port.
Help please..... :)
Thanks in advance.
Nubin Stanley
You can use udev rules to create symbolic links just to your device:
(these rules go in /etc/udev/rules.d/-name.rules -- look at your udev documentation
KERNEL=="ttyUSB*", ATTRS{idVendor}=="<vendorid>", MODE="0666", SYMLINK+="mydev"
You have to specify your vendor id and/or product id for your device. Then those devices will be available at /dev/mydev in the above example.
You can also use various other parameters to create appropriate unique symbolic links for your use. Check udev man page.
Here's my code, based on Alex Robinson's, but without global "except":
import os
from os.path import join
def find_tty_usb(idVendor, idProduct):
"""find_tty_usb('067b', '2302') -> '/dev/ttyUSB0'"""
# Note: if searching for a lot of pairs, it would be much faster to search
# for the enitre lot at once instead of going over all the usb devices
# each time.
for dnbase in os.listdir('/sys/bus/usb/devices'):
dn = join('/sys/bus/usb/devices', dnbase)
if not os.path.exists(join(dn, 'idVendor')):
continue
idv = open(join(dn, 'idVendor')).read().strip()
if idv != idVendor:
continue
idp = open(join(dn, 'idProduct')).read().strip()
if idp != idProduct:
continue
for subdir in os.listdir(dn):
if subdir.startswith(dnbase+':'):
for subsubdir in os.listdir(join(dn, subdir)):
if subsubdir.startswith('ttyUSB'):
return join('/dev', subsubdir)
This Python code seems to find the /dev/ttyUSB number for the given vendor ID and product ID. Not hard to translate it to C. Parsing the output from hwinfo --usb can do the trick, too. The regx is:
"\s\sVendor:\susb\s0x([0-9a-f]{4}).*?\s\sDevice:\susb\s0x([0-9a-f]{4}).*?\s\sDevice\sFile:\s/dev/ttyUSB([0-9]+)"
import glob
import os
import re
def find_usb_tty(vendor_id = None, product_id = None) :
tty_devs = []
for dn in glob.glob('/sys/bus/usb/devices/*') :
try :
vid = int(open(os.path.join(dn, "idVendor" )).read().strip(), 16)
pid = int(open(os.path.join(dn, "idProduct")).read().strip(), 16)
if ((vendor_id is None) or (vid == vendor_id)) and ((product_id is None) or (pid == product_id)) :
dns = glob.glob(os.path.join(dn, os.path.basename(dn) + "*"))
for sdn in dns :
for fn in glob.glob(os.path.join(sdn, "*")) :
if re.search(r"\/ttyUSB[0-9]+$", fn) :
#tty_devs.append("/dev" + os.path.basename(fn))
tty_devs.append(os.path.join("/dev", os.path.basename(fn)))
pass
pass
pass
pass
except ( ValueError, TypeError, AttributeError, OSError, IOError ) :
pass
pass
return tty_devs
print find_usb_tty()
The best way to do this is would be to use libusb, but if that doesn't give you enough information about your devices (which it may not), then you'll have to use the /proc filesystem which the kernel makes available, specifically /proc/bus/usb/.
Have a read of this information on /proc/bus/usb: in particular on /proc/bus/usb/devices. But as you say, this is all a bit hacky!