[lustre-devel] [PATCH 17/37] lustre: simplify lprocfs_read_frac_helper.
Andreas Dilger
adilger at whamcloud.com
Tue Feb 26 17:06:47 PST 2019
On Feb 26, 2019, at 16:59, NeilBrown <neilb at suse.com> wrote:
>
> On Sun, Feb 24 2019, James Simmons wrote:
>
>>> This function seems overly complex, the same functionality
>>> is available with much less effort.
>>
>> Actually we are in discussion about removing these functions.
>> The details are at:
>>
>> https://jira.whamcloud.com/browse/LU-11157
>>
>> Since shells typically don't handle "floating point" representation
>> well you can see the following:
>>
>> sanity 64d with the same error message; '209.9: syntax error: invalid
>> arithmetic operator (error token is ".9")'
>>
>> The second issues is that the read values are not true representation
>> of the desired value. The same issues is with the string helpers as
>> well. Take for example
>>
>> test_string_get_size_one(1100, 1, "1.10 kB", "1.07 KiB");
>>
>> Which is taken from linux/lib/test-string_helpers.c.
>>
>> If you pass 1100 to string_get_size() you can get either 1.10 kB or 1.07
>> KiB. Now if do the reverse 1.10 kB you get ~1126 which is not the same as
>> 11000. I discussed how to handle this problem with Andreas and he agreed
>> the best solution is make all the sysfs / debugfs *_mb files turn any
>> values passed in to around up to the nearest MiB. This way we can report
>> the exact MiB settings to the users. We already have a patch to do this
>> for max_dirty_mb which I can push. The other *_mb files need to be updated
>> to round off. If you can wait a few days I can backport the already done
>> patch and push a patch for the rest.
>
> My recommendation would be to deprecate all _mb files and instead have
> _bytes files which report a simple integer - the number of bytes.
That would break a lot of configurations and documentation. Also, bytes
are not very convenient units for a lot of the numbers, for example you
don't want to (nor could you) send 47-byte RPCs.
> Leave all the unit conversion to user-space.
>
> Linus once told me that he prefers sysfs files to always be in basic
> units, and that decimals are fine. So use "seconds" for time, even if
> that means 0.002 for 2 milliseconds. Use bytes for storage, etc.
That is not going to be better than allowing "max_dirty_mb=0.5", which
is what we wanted to get rid of in the first place. Back in the day
when a system had 4MB DIMMs it was useful to allow fractional MB for the
cache size or debug log size, but I don't think that is useful today.
I'm content to just round these to the nearest MB, in the rare case that
someone specifies a fractional unit, but honestly I don't think that
anyone does anymore. It is much more likely they will be setting the
cache size to 16G per target on their 256GB RAM nodes.
Cheers, Andreas
>>> Signed-off-by: NeilBrown <neilb at suse.com>
>>> ---
>>> .../lustre/lustre/obdclass/lprocfs_status.c | 47 +++-----------------
>>> 1 file changed, 7 insertions(+), 40 deletions(-)
>>>
>>> diff --git a/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c b/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
>>> index 568e6623e0c8..bd24e48f6145 100644
>>> --- a/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
>>> +++ b/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
>>> @@ -205,53 +205,20 @@ static void obd_connect_data_seqprint(struct seq_file *m,
>>> int lprocfs_read_frac_helper(char *buffer, unsigned long count, long val,
>>> int mult)
>>> {
>>> - long decimal_val, frac_val;
>>> int prtn;
>>>
>>> if (count < 10)
>>> return -EINVAL;
>>>
>>> - decimal_val = val / mult;
>>> - prtn = snprintf(buffer, count, "%ld", decimal_val);
>>> - frac_val = val % mult;
>>> -
>>> - if (prtn < (count - 4) && frac_val > 0) {
>>> - long temp_frac;
>>> - int i, temp_mult = 1, frac_bits = 0;
>>> -
>>> - temp_frac = frac_val * 10;
>>> - buffer[prtn++] = '.';
>>> - while (frac_bits < 2 && (temp_frac / mult) < 1) {
>>> - /* only reserved 2 bits fraction */
>>> - buffer[prtn++] = '0';
>>> - temp_frac *= 10;
>>> - frac_bits++;
>>> - }
>>> - /*
>>> - * Need to think these cases :
>>> - * 1. #echo x.00 > /sys/xxx output result : x
>>> - * 2. #echo x.0x > /sys/xxx output result : x.0x
>>> - * 3. #echo x.x0 > /sys/xxx output result : x.x
>>> - * 4. #echo x.xx > /sys/xxx output result : x.xx
>>> - * Only reserved 2 bits fraction.
>>> - */
>>> - for (i = 0; i < (5 - prtn); i++)
>>> - temp_mult *= 10;
>>> -
>>> - frac_bits = min((int)count - prtn, 3 - frac_bits);
>>> - prtn += snprintf(buffer + prtn, frac_bits, "%ld",
>>> - frac_val * temp_mult / mult);
>>> + prtn = snprintf(buffer, count, "%ld.%02lu",
>>> + val / mult,
>>> + (val % mult) / (mult / 100));
>>>
>>> + /* Strip trailing zeroes, and trailing '.' */
>>> + while (prtn && buffer[prtn-1] == '0')
>>> + prtn--;
>>> + if (prtn && buffer[prtn-1] == '.')
>>> prtn--;
>>> - while (buffer[prtn] < '1' || buffer[prtn] > '9') {
>>> - prtn--;
>>> - if (buffer[prtn] == '.') {
>>> - prtn--;
>>> - break;
>>> - }
>>> - }
>>> - prtn++;
>>> - }
>>> buffer[prtn++] = '\n';
>>> return prtn;
>>> }
Cheers, Andreas
---
Andreas Dilger
Principal Lustre Architect
Whamcloud
More information about the lustre-devel
mailing list