Dear all, I did some performance tests that made me really wonder:
My Hardware: Asus P5LD2 board with Intel i945P chipset, ICH7R southbridge CPU Intel Core 2 Duo E6300 at 1.86 GHz, 2 MB Cache 1 GB RAM My Software: OpenSuSE 10.2 with Linux kernel 2.6.18, x86-64 architecture FreeBSD 6.2 Testdrives: 1. HDD: Seagate ST3250820AS RPM 7200.9, 8 MB Cache, 250 GB, SATA-II (Harddisk Drive) 2. SSD: Adtron AF25FB, 27GB, SATA Revision 1.0a (Solid State Disk) What I did: I wrote blocks of 1 MB size to file. Each 1 GB I made a fsync and took the time. For those tests with filesystems I wrote files of 1 GB size, otherwise I just wrote to the raw device. Results: -1- Test OpenSuSE(AHCI) FreeBSD(AHCI) --------------------------------------------------------------------------------------------------------------------------------------- SSD(vfat 25GB) 41+/-2 MB/s at 4-10% 15+/-0 MB/s at 2% CPU SSD(raw 25GB) 26+/-1 MB/s at 4-10% CPU 48+/-0 MB/s at 1% CPU SSD(ext3 25GB) 39+/-5 MB/s at 10-15% CPU 34+/-0 MB/s at 14% CPU SSD(ext2 25GB) 42+/-1 MB/s at 10-15% CPU 32+/-0 MB/s at 10% CPU --------------------------------------------------------------------------------------------------------------------------------------- Test OpenSuSE (AHCI off) FreeBSD (AHCI off) --------------------------------------------------------------------------------------------------------------------------------------- SSD(vfat 25GB) 22+/-4 MB/s at 6-19% CPU -- SSD(raw 25GB) 33+/-4 MB/s at 7-14% CPU 41+/-0 MB/s at 1% CPU SSD(ext2 25GB) 27+/-6 MB/s at 6-14% CPU -- --------------------------------------------------------------------------------------------------------------------------------------- Question 1: Can anybody explain to me, why writing to a SATA-I device with AHCI consumes so much CPU time using Linux, while it takes almost no CPU time on FreeBSD 6.2 ? Especially comparing values of writing to the raw device? Question 2: Can anybody explain to me, why writing to a solid state disk (a kind of memory that always has the same constant bandwidth) has such big standard errors in writing rate using Linux (between 1 to 6 MB/s error) while FreeBSD gives an almost constant writing rate (as one would expect it for a SSD) ? Question 3: Why is writing to a raw device in Linux slower than using e.g. ext2 ? And why is Linux writing rate much lower (-12.5 % for the best case) compared to writing rate of FreeBSD? Question 4: When writing to the SATA-II HDD Linux is around 10% slower than FreeBSD when using ext3, but around as fast as FreeBSD when writing raw. Why? How can I improve the speed of Linux, Thanks for advices Martin PS: part of my testcode: int fd=open(fileName, O_WRONLY | O_CREAT | O_TRUNC, 0666); (void)gettimeofday(&start, 0); for (long bl=0; bl < blocksPerGigaByte; ++bl) write(fd, block, blockSize); fsync(fd); (void)gettimeofday(&ende, 0); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
